Class 9

Haryana State Board HBSE 9th Class Science Important Questions Chapter 11 Work and Energy Important Questions and Answers.

Haryana Board 9th Class Science Important Questions Chapter 11 Work and Energy

Very Short-Answer Type Questions

Question 1.
What is work ?
Answer:
When force is applied on an object and it moves in the direction of force, it is said to be work done.

Question 2.
On which the quantity of work depends ?
Answer:
The quantity of work depends upon the applied force & distance moved.

Question 3.
What is the formula of work ?
Answer:
Work = Force x Displacement.

Question 4.
What is the unit of work ?
Answer:
Newton-metre (Joule).

Question 5.
What is energy ?
Answer:
The capacity of doing work is called energy.

Question 6.
What are the types of mechanical energy ?
Answer:
Mechanical energy is of two types:
(1) Kinetic energy,
(2) Potential energy.

Question 7.
What is potential energy ?
Answer:
The energy possessed by a body due to its position or change in shape is called potential energy.

Question 8.
Which type of energies are in aircraft flying on height ?
Answer:
Both type of energies-kinetic and potential.

Question 9.
Which type of energy is there in a stone lying on a hill ?
Answer:
Potential energy.

Question 10.
What is mechanical Energy ?
Answer:
The sum of kinetic energy and potential energy of a body is called mechanical energy.

Question 11.
Which type of energy is there when a bullet is fired from a gun ?
Answer:
Kinetic energy.

Question 12.
Write the formula for kinetic energy.
Answer:
Kinetic energy = \(\frac {1}{2}\) mv², where m → mass, v → velocity.

Question 13.
Write the formula for potential energy.
Answer:
Potential energy = mgh, where m → mass, g → acceleration due to gravity and h → height.

Question 14.
What is the law of conservation of energy ?
Answer:
According to this law, energy can neither be created nor be destroyed but can only be transferred from one form to another.

Question 15.
What is the effect on energy when work is done ?
Answer:
When work is done, energy decrease in some extent.

Question 16.
What is the work done by a man when he lifts a luggage of mass 10 kg on his head and moves 50 metres on horizontal road ?
Answer:
zero.

Question 17.
From where, our body gets energy ?
Answer:
From food taken by us.

Question 18.
Which type of energy is used by plants ?
Answer:
Solar energy.

Question 19.
Write an important use of wind energy.
Answer:
Wind energy is used to grind the flour by wind mills.

Question 20.
Write the name of any two natural sources of energy.
Answer:
(i) Sun
(ii) Water.

Question 21.
Write any four types of energy.
Answer:
(i) Mechanical Energy
(ii) Chemical Energy
(iii) Light Energy
(iv) Sound Energy.

Question 22.
What is gravitational potential energy ?
Answer:
The energy stored in a body when work is done against force of gravity is called gravitational potential energy.

Question 23.
What is mean by elastic potential energy ?
Answer:
The energy possessed by an object due to change in its shape is called elastic potential energy.

Question 24.
Why spark is produces when two stones collides with each other ?
Answer:
Because kinetic energy of stone is converted into light energy.

Question 25.
How arrow gets its kinetic energy ?
Answer:
The arrow converts the potential energy from bow into kinetic energy.

Question 26.
Out of energy and acceleration, which is vector ?
Answer:
Acceleration is a vector quantity.

Question 27.
The kinetic energy goes on decreasing when it is thrown vertically upward. What will be the motion at highest point ?
Answer:
Zero.

Question 28.
Write the name of that device which converts electric energy into mechanical energy.
Answer:
Electric motor.

Question 29.
Which energy is converted in other in a hydroelectric power centre ?
Answer:
The kinetic energy of water is converted into electric energy.

Question 30.
What is power ? What is its unit ?
Answer:
The rate of doing work is power. Its unit is watt.

Question 31.
If the velocity of an object is increased three times, what will be its kinetic energy ?
Answer:
The kinetic energy will increase nine times.

Question 32.
Which type of energy is there in a expanded spring ?
Answer:
Potential energy.

Question 33.
Which type of energy is there in a dam ?
Answer:
Potential energy.

Question 34.
Which type of energy is there in the spring of watch ?
Answer:
Potential energy which gives the kinetic energy to the needles of watch. ,

Question 35.
Which type of energy is there in running train ?
Answer:
Kinetic energy.

Question 36.
What will be potential energy of that body whose height is doubled ?
Answer:
Its potential energy will be doubled.

Question 37.
What is the relation between 1 kilowatt and watt ?
Answer:
1 kilowatt = 1000 watt.

Question 38.
Why the palms become hot when rubbed ?
Answer:
Because kinetic energy of palms is converted into heat energy.

Question 39.
How much energy is required to lift a stone of mass 1 kg to a height of 1 metre ?
Answer:
9.8 Joules [∵ W = mgh = 1 x 9.8 x 1 = 9.8 joules]

Question 40.
A person and his son are running with uniform velocity. If the mass of person become two times more than of his son, then what will be the ratio between kinetic energy of both ?
Answer:
2 : 1 [ ∵ K.E. = \(\frac {1}{2}\) mv² and v is equal]

Question 41.
Which type of energy is required to move for a sailboat ?
Answer:
The sailboat moves by the kinetic energy of wind.

Question 42.
What will be the energy a body has a capacity to do a work of 10 joules ?
Answer:
10 Joules.

Question 43.
Write the name of two units of power used in daily life.
Answer:
Kilowatt and megawatt.

Question 44.
How many watts are there in one horse power ?
Answer:
1 horse power = 746 watt.

Question 45.
What is meant by 1 kilowatt hour energy ?
Answer:
The energy consumed by a source of 1 kilowatt power in 1 hour.

Question 46.
What is the relation between kilowatt hour and joule ?
Answer:
1 kilowatt hour = 36,00,000 joules.

Question 47.
Which type of energy is used when a person climbs stairs ?
Answer:
Muscular energy.

Question 48.
Which type of energy is there in our body ?
Answer:
Chemical energy.

Question 49.
The person requires the least amount of energy in which of the following activity ?
(i) In swimming
(ii) In movement
(iii) In sleeping
(iv) In running foot.
Answer:
(iii) In sleeping.

Question 50.
What is simple pendulum ?
Answer:
Simple pendulum is a metalic bob which is hang by weightless string.

Question 51.
Write the name of energy when simple pendulum is at its extreme point.
Answer:
Potential energy.

Question 52.
Write the name of energy when pendulum is in middle position.
Answer:
Kinetic energy.

Short-Answer Type Questions

Question 1.
What is meant by work ? How is it measured ? What is its unit ?
Answer:
Work done on an object is defined as the magnitude of the force multiplied by the distance moved by the object in the direction of the
applied force.
Thus, Work done = Force x The distance moved in the direction of force
W = F x s
Work is a vector quantity. Unit of work is newton-metre or joule (J).

Question 2.
What is energy ? Write its unit and definition. What are its various types ?
Answer:
The capacity of doing work is energy. Its unit is also joule.
Joule: Work done is said to be one joule when a force of 1 newton acting on an object and the object is displaced through 1 m in the direction of force.

Various types of energy:
(i) Mechanical energy
(ii) Heat energy
(iii) Chemical energy
(iv) Electric energy
(v) Nuclear energy’
(vi) Light energy
(vii) Atomic energy
(viii) Magnetic energy
(ix) Sound energy,
(x) Solar energy.

Question 3.
Justify with example that moving bodies have capacity to do work ?
Answer:
The examples are following :
(i) A moving marble has a capacity to displace that marble which is in rest.
(ii) The blowing wind works by rotating the wheels of windmill.
(iii) The moving water also takes the objects from one place to another.
(iv) The blowing wind is helpful for sailing boat.
Thus, we can say that moving bodies have capacity to do work.

Question 4.
What is meant by potential energy and kinetic energy ? Give two examples for each.
Answer:
Potential energy’: The energy possessed by a body due to its change in position or shape is called the potential energy.
Examples:
(1) The book lying on the table has potential energy due to its position.
(2) A binded watch has potential energy.

Kinetic energy:
The energy possessed by a body due to its motion is called the kinetic energy.

Examples:
(1) Moving air has kinetic energy.
(2) The running water has kinetic energy.

Question 5.
Is there energy in following substances ? If yes, then what is the type-potential energy or kinetic energy or both ?
(i) The switched off ceiling fan.
(ii) A man climbing up mountain.
(iii) Flying bird.
(iv) The water in a dam.
(v) The stretched bow more than its shape.
(vi) The rubber locket on a table.
(vii) Stretched locket of rubber.
Answer:
Yes, all substances have energy’.
(i) A switched off ceiling fan has potential energy only.
(ii) A man climbing up mountain has both potential and kinetic energy.
(iii) A flying bird has both kinetic and potential energy.
(iv) The water in the dam has potential energy.
(v) A stretched bow has potential energy.
(vi) The rubber locket on the table has potential energy.
(vii) Stretched locket of rubber has potential energy.

Question 6.
Write the difference between potential energy and kinetic energy.
Answer:
The differences between potential energy and kinetic energy are as follows:
Potential Energy (P.E.):
1. The energy possessed by an object due to its position is called potential energy.
2. Potential energy = mgh
3. The potential energy of an object depends upon the height or depth from the surface of earth.

Kinetic Energy (K.E.):
1. The energy possessed by an object due to its motion is called kinetic energy.
2. Kinetic energy = \(\frac {1}{2}\) mv²
3. Kinetic energy depends upon the motion of the object.

Question 7.
Which type of energy is in following ?
(1) Coiled spring of watch.
(2) Running buffallo.
(3) The arrow released from bow.
(4) A table lying on roof.
(5) Compressed air.
(6) A mango on tree.
Answer:
(1) Potential energy
(2) Kinetic energy
(3) Kinetic energy
(4) Potential energy
(5) Potential energy
(6) Potential energy.

Question 8.
When the capacity of doing work by human body decreases ?
Answer:
The capacity of doing work by human body decreases in following circumstances :
(1) When a person is ill.
(2) When a person grows old.
(3) When a person takes food less than required, his muscular energy decreases.

Question 9.
What is the relation between work and energy ? Write their units.
Answer:
The capacity of doing work is called energy. The magnitude of energy is always equal to that work which has a capacity to do that. Energy is measured in joule and the unit of work is also joule.

For example:
To lift a piece of stone of mass 1 kg upto a height of 1 metre requires 9.8 joules energy. Opposite to it, when stone is dropped from one metre, the stone does the same amount of work (9.8 J). Thus, if an object has an energy of 100 joules. It has a capacity of doing work of 100 joules.

Question 10.
How the energy is transferred in key toy ?
Answer:
There is a spring in key toy or key watch which contracts while binding and stored potential energy in it. After some moments, the spring loses slowly and the toy comes in motion. Thus, potential energy is transferred in kinetic energy.

Question 11.
A ball is thrown upward and it returns back. What is the change in kinetic and potential energy of the ball ? Explain.
Answer:
When a ball is thrown upward its kinetic energy changes continuously into potential energy. At highest point its whole kinetic energy changes into potential energy. When the ball returns back its potential energy changes continuously into kinetic energy and whole of its potential energy changes into kinetic energy near the earth but on reaching the earth, whole of its kinetic energy changes into potential energy.

Question 12.
A boy is standing by holding some weight in his expanded hand. In this stage, there seems no change in the position of both boy and weight. Is he doing any work ? If yes, then justify.
Answer:
Yet, there is no change in the position of boy and weight externally, but internally the boy is working. The muscles of boy are stretched due to weight on palm. Thus, their shape get changes. The heart pumps more blood into muscles. The energy of boy wastes in all these chemical activities and he tired soon. If the boy stand more enough in same position, the external change will be observed as sweating.

Question 13.
How much work is done when an artificial satellite revolve round the earth ? Explain in brief. –
Answer:
The artificial satellite revolves round the earth in almost circular track. The gravitational force between the earth and the satellite works along the line joining the earth and satellite and the satallite moves perpendicular to the direction of force of gravity. Thus, the magnitude of displacement of satellite in the direction of force will be zero and the work done by the earth on the satellite will also be zero.

Question 14.
How the kinetic energy of wind is utilised ? Write its important uses.
Answer:
The electric energy can be produced by the energy in the blowing air. It has much waste. Thus, wind mill is used in grinding flour and drawing out water from ponds. A small amount of electric energy is produced from wind mill. Those places where the wind blows throughout the years, wind mill are used to grind flour and drawing out water.
Important uses of mechanical energy of wind :
(1) The fields can be irrigated by drawing water from ponds.
(2) It can be used in grinding the flour.
(3) The mechanical energy of wind can be converted into electric energy by joining the various wind wheels together.

Question 15.
What is water energy ? Write its two important uses.
Answer:
The running water has a capacity to do work due to its kinetic energy, which is known as water energy.

Uses of water energy: Following are the uses of water energy :
(1) Water energy is converted into electric energy and it is used in houses and factories.
(2) Water energy is used to grind flour by windmills.
(3) The heavier wooden pieces is taken from one place to another due to water energy.

Question 16.
How water energy is used to produce electricity ?
Answer:
The kinetic energy of running water is stored as potential energy in dam. The stored water is dropped on the larger blades of water turbines. The shaft attached with running turbine rotates the generator or dyanmo quickly. The rotating coil of dyanmo produces electricity which is called ‘hydroelectric power’. The electricity is produced on Bhakhra dam by this method. This is also known as the principle of hydroelectricity.

Question 17.
Why the nail becomes hot when it is hammered in the sheet of wood ?
Answer:
The nail becomes hot when it is hammered in the sheet of wood because the lifted hammer has potential energy due to its position. When the hammer is dropped on the nail, it comes in rest position, but transfers, its whole energy in the nail. As a result of this, the nail gets some kinetic energy and moves inside the wood. When the nail enters completely and we continuous hammering the nail becomes hot because the mechanical energy of the hammer is transferred in nail and changes into heat energy.

Question 18.
What are the benefits of the solar energy ?
Answer:
The benefits of the solar energy are as follows :
(1) The solar energy is used in solar cooker to prepare food,
(2) Solar energy is used to warm the water by solar heater in hotels, hospitals and industries.
(3) Solar energy is used in the production of electricity.
(4) It is used to melt the metals in solar furnances.

Question 19.
Differentiate among work, energy and power. Write the SI unit for each. Or What is Power? Write its S.I. unit.
Answer:
Work:
When force is applied on a body and it moves in the direction of force, it is said to be work done.
Thus, Work (W) = Force (F) x Distance (S)
SI unit of work is joule.

Energy: t he capacity ot doing work is called energy. SI unit of energy is joule.

Power: The rate of doing work is called power.
Thus,

SI unit of power is watt.

Question 20.
What do you mean by transfer of energy ? Write two examples of transfer of energy.
Answer:
According to the law of conservation of the energy, The energy can neither be created nor destroyed. It can be transferred from one form to another. It is called the transfer of energy. Thus, the total magnitude of energy is never changed.

Examples:
(1) Ice on mountains melts and becomes water. This is the transfer of potential energy into kinetic energy.
(2) The electric energy in bulb changes into light energy and glows.

Numerical Questions

Question 1.
A boy of mass 40 kg is running with a ve’ocity of 0.5 ms. What is his kinetic energy ?
Solution:
Here,
m = 40 k
v = 0.5 ms^-1
We know that,
Kinetic Energy (K.E.) = \(\frac {1}{2}\) mv²
= \(\frac {1}{2}\) x 40 x 0.5 x 0.5 = 5 Joule Answer:

Question 2.
An object of mass 15 kg is moving with a uniform velocity (if 4 ms. What is tue kincth energy possessed by the object?
Solution:
Here
Mass of the body (m) = 1 5 kg
Velocity of the body (v) = 4 rn/s
We know that
Kinetic Energy (K.E) = \(\frac {1}{2}\) mv²
= \(\frac {1}{2}\) x 15 x 4(2)²
= \(\frac {1}{2}\) x 15 x 16
= 120 Jule

Question 3.
A stone of mass 100 gram is kept at a height ofS metre. What kind of energy does it possess and find out its value.
Solution:
The stone has potential energy because of height.
Here. m = 100g = \(\frac {100}{1000}\) = 0.1 kg
g = 9.8 ms^-2
h = 5m
We know that.
Potential Energy (P.E.) m x g x h = 0.1 x 9.8 x 5 = 4.9 Joule

Question 4.
To what height can an object of mass 1 kg be raised by giving it an energy of 980 joule?
Solution:
Here.
m = 1 kg
g = 9.8 ms^-2
h = ?
Potential Energy (RE.) = 980 J
We know that,
Potential Energy (RE.) = m.g.h.
or 980 = 1 x 9.8 x h
or h = \(\frac{980}{1 \times 9.8}\)
= 100 m

Question 5.
What is the increase in kinetic energy of a particle, if its velocity is increased to four times?
Solution:
Suppose the initial velocity of the particle = v
and its final velocity = 4 v
Suppose the mass of the particle = m
∴Initial kinetic energy (K₁) of the particle = \(\frac {1}{2}\) mv² ………….(i)
Final kinetic energy (K₂) of the particle = \(\frac {1}{2}\)m (4v)²
= \(\frac {1}{2}\)m x 16 v² …………..(ii)
From equations (i) and (ii),
\(\frac{\mathrm{K}_1}{\mathrm{~K}_2}=\frac{\frac{1}{2} \mathrm{mv}^2}{\frac{1}{2} \mathrm{~m} \times 16 \mathrm{v}^2}=\frac{1}{16}\)
or K₂ = 16K₁
Thus, the increase in kinetic energy is 16 times the initial kinetic energy.

Question 6.
The kinetic energy of a ball of mass loo g is 20 joule. Calculate its velocity.
Solution:
Here,
m = 100 g = \(\frac {100}{1000}\)kg = 0.1 kg
v = ?
Kinetic Energy (K.E.) = 20 J
We know that, Kinetic Energy (K.E) = \(\frac {1}{2}\) mv²
Or 20 = \(\frac {1}{2}\) x 0.1 x v²
v² = \(\frac {20 x 2}{0.1}\) = 400
or v = \(\sqrt{400}\) = 20 ms^-1

Question 7.
A coolie lifts an object of mass 20 kg from the earth to 1.5 m and keep It on his head. Calculate the amount of work done by him on the object.
Solution:
Here,
Mass of the object (m) = 20kg
Displacement (s) = 1 .5m
Work done (W) = F x s = mg x s
= 2okg x 10 ms^-2 x 15 m
= 300kgms^-2 m
= 300Nm= 300J
The amount of work done by the coolie on the object is 30 joules.

Question 8.
A man of mass 50 kg jumps to a height of 1.2 m. What is its potential energy at the highest point?
Solution:
Here,
m = 50kg
g = 9.8 ms^-2
h = 12m
We know that,
Potential Energy (P.E.) m x g x h
= 50 x 9.8 x 1.2
= 588 J
Thus, at the highest point the potential energy of the man is 588 J.

Question 9.
With what velocity should a man of mass 50 kg run so that his kinetic energy becomes equal to 625 J.
SolutIon:
Here,
m = 50kg
v = ?
Kinetic Energy (K.E.) = 625 J
We know that,
Kinetic Energy (K.E) = \(\frac {1}{2}\) mv²
Or 625 = \(\frac {1}{2}\) x 50 x v²
v² = \(\frac{625 \times 2}{50}\) = 25
or v = \(\sqrt{25}\) 5ms

Question 10.
A man throws a stone of mass 10 kg from a ladder of height 5m. When ¡t reaches the ground, what will be its kinetic energy ? What will be its velocity at the nearest point to the ground?
Solution:
Here,
m = 10kg
h = 5m
v = ?
Kinetic Energy (K.E.) = ?

We know that,
The kinetic energy (K.E.) of the stone = The loss in potential energy due to falling of the stone
= mgh
= 10 kg x 9.8 ms^-2 x 5m = 490J ……………(i)
Because kinetic energy = \(\frac {1}{2}\) mv² .(ii)
From eqns. (i) and (ii),
\(\frac {1}{2}\) mv^-2 = 490J
or \(\frac {1}{2}\) x 10kg x v² = 490J
or v² =\(\frac{490 \times 2}{10}=\frac{980}{10}\) = 98
or v = \(\sqrt{98}\) = 9.9 ms^-1 (approx.)

Question 11.
A car of mass 1000 kg is moving with a velocity of 30 ms^-1. After applying brakes it stops with uniform acceleration at a distance of 50m. Calculate the force and the work done by the brakes?
Solution:
Here,
m = 1000kg
u = 30 ms^-1
v = 0 ms^-1
s = 50m
F = ?
W = ?
We know that, v² – u² = 2as
a = \(\frac{v^2-u^2}{2 s}=\frac{(0)^2-(30)^2}{2 \times 50}=\frac{-900}{100}\) ms^-2
= – 9 ms^-2 So retardation = 9ms^-2
F = m.a.l000kg x 9ms² = 9000 N
The force applied by the brakes on the car (F) = 9000 N
Work done(W) = F x s = 9000 N x 50 m = 450000 J = 450 kJ

Question 12.
A man of mass 50kg climbs a vertical height of 10m on a mountain in 20 seconds. What ¡s his power ? (Given that g 9.8 ms-2)
Solution:
Here,
F = m x g
= 50 x 9.8 = 490N
Now, W = F x S = 490N x 10m = 4,900 Nm
Time (t) = 20 seconds
Power (P) = \(\frac{\text { Work done }}{\text { Time taken }}=\frac{4,900}{20}\) = 245 watt

Question 13.
A boy of mass 40 kg runs up a staircase of 45 steps in 9 sec. If the height of each step is 15 cm, Calculate his power ? (The value of g is 10 ms²)
Solution:
Weight of the boy (mg) 40kg x 10ms² = 400N
Total height of the steps (h) = 45 x 15/100m = 675m
Time taken to climb the steps (t) = 9s
We now that
Power (P) = Time taken = \(\frac{\mathrm{mgh}}{t}\) = \(\frac{400 \mathrm{~N} \times 6.75 \mathrm{~m}}{9 \mathrm{~s}}\) = 300 W
The power of the boy is 300 W.

Question 14.
A man of mass 50 kg climbs 30 steps in 30 sec. If height of each step is 20 cm. Then calculate the power to climb the total steps.
Solution:
Mass of the man (m) = 50 kg
Total number of steps = 30
height of each step = 20 cm = \(\frac {20}{100}\) m = 0.2 m
Total height covered by the man = 30 x 0.2 m = 6m
Acceleration due to gravity (g) = 10 ms^-2
Thus, work done by the man = m.g.h = 50 x 10 x 6J = 3000J
Time taken to climb the steps = 30 s

= \(\frac{3000 \mathrm{~J}}{30 \mathrm{~s}}\)
= 100 Js^-1 = 100 W(watt)

Question 15.
An electric bulb of 100 Wis used for 2 hours, how much electrical energy is consumed?
Solution:
Power of the bulb = 100W
Time = 2 hours 2 x 3600 = 7200 sec.
Energy consumed = Power x Time
= 100 x 7200Ws = 720000 joule

Question 16.
A rocket has a mass of 3 x 10⁶ kg. Calculate (a) its potential energy (b) its kinetic energy, at a height of 25 km moving with a velocity of 1 km/s. (Take g = 10 ms^-2)
Solution:
Here,
Mass of the rocket (m) 3 x 10⁶ kg
Velocity of the rocket (v) = 1 k ms^-1 = 1000 ms^-1
Height of the rocket (h) = 25 km = 25000 m
Acceleration due to gravity (g) = 10 ms^-2

(a) Potential Energy = m.g.h.
3 x 10⁶ x 10 x 25000 J
= 7.5 x 10¹¹

(b) Kinetic Energy = \(\frac {1}{2}\) mv²
= \(\frac {1}{2}\) x 3 x 10⁶ x (1000)² J
= 7.5 x 10¹¹J

Question 17.
A horse is pulling a cart moving with a velocity of 18 kmh^-1 with a force of 300 N. Find out the power of the horse in watt and also in horse power?
Solution:
Here,
Velocity of the cart(v) = 18 kmh^-1
= \(\frac{18 \times 1000}{3600}\) ms^-1 = 5 ms^-1
The force exerted by the horse on cart (F) = 300 N
m.g. = 300N
Work done = m.g.h
= 300 x 5 = 1500J

= \(\frac{15000}{1s}\) = 1500 w
We know that, 746 W = 1 horsepower
1 waft = \(\frac {1}{746}\) horsepower
1500 watt = \(\frac {1}{746}\) x 1500 horsepower
= 2 horsepower

Do Yourself

(1) A car is moving with a uniform velocity of 54 kmh^-1 What will be the kinetic energy of a child of mass 40 kg sitting inside it?
Answer:
[4500J]

(2) Calculate the power of that pump which stores the water of loo kg in 25 seconds into a tank kept at a height of 19m. (Let g = 10 ms²)

(3) What will be the energy of an object of mass 10 kg at a height of 40 m from the ground level?
Answer:
[Take g 100 ms²] [40003]

(4) A force of 5 N is acting on a body. The body displaces to a distance of 2m in the direction of the force. Find out the work done on the object.
Answer:
[103)

(5) An object of mass 15 kg is moving uniformly with a velocity of 4 ms². Calculate the kinetic energy of the object.
Answer:
[120J]

(6) What will be the height from the ground level where an object of mass 1 kg will have a potential energy of 1 joule if g= 10 ms²?
Answer:
[0.1 m]

(7) If 4900 joule of energy is utilised in lifting a body of mass 50 kg to a certain height, then what will be the height of the object if g = 9.8 ms²?
Answer:
[10m]

(8) A body of mass 3 kg starts falling down from rest position. After 3 sec., what will be its kinetic energyifgl0m.c2?
Answer:
[1350m]

(9) An object of mass 10 kg is lifted to a height of 6m from the ground level. Calculate the energy present in the object. The value of g is
9.8 ms².
Answer:
[588 J]

(10) An object of mass 12 kg is kept at a certain height. 1f its potential energy is 480 J; calculate its height from the ground level.
Answer:
[Take g = 10 ms²] [4 m]

(11) A man of mass 50kg takes a packet of mass 20kg upto the terrace of a building of height 14m, what is the work done by the man ?
Answer:
[Take g = 10 ms²] [9604 J]

(12) A vehicle of mass 1800 kg is moving with a velocity of 40 ms. After applying brakes it stops with a uniform acceleration at a distance of 200 m. Calculate the force applied and work done by the brakes.
Answer:
[1440 kJ]

(13) What will be the increase in kinetic energy of a particle if its velocity is doubled?
Answer:
[4 times ]

(14) How much amount of work is done on lifting an object of mass 2 kg to a height of 2m if the value of g is 9.8 ms²?
Answer:
[39.2J1

(15) The height of’Kutubminar’ is 70m. What is the work done by a man of mass 50 kg on reaching the top?
Answer:
[Take g 9.8 ms^-2] [3430011

(16) A stone of mass 10g is kept at a height of 5m. What kind of energy is present in it and calculate its value?
Answer:
[Take g 9.8 ms^-2] [0.49J]

(17) Two girls A and B of mass 400 N each, climbs a rope upto a height of 8m. IfA takes 20 sec. to do this work while B takes 50 sec.,
then calculate the individual power of both the girls.
Answer:
[A 160 W, B = 64W]

(18) Find the energy in KWh consumed inS hours by four devices of power 500 W each.
Answer:
[10Kwh]

Essay Type Questions

Question 1.
Define potential energy. Derive an expression for the potential energy of a body.
Answer:
Potential Energy:
The energy possessed by a body due to its position or change in shape is known as potential energy.

Expression for potential energy:
Consider a body of mass m kept on the.ground level at point ‘A’. it is raised to a point ‘B’ by applying a force F on it. The distance between A and B is ‘h’.
As we know that, the force F acting on the body to lift it, is equal and opposite to the gravitational force
F = \(\frac{G M_e m}{\mathrm{R}_e{ }^2}\) …………(i)

Where, M_e = Mass of the earth
R_e = Radius of the earth
But, g = \(\frac{G M_e m}{\mathrm{R}_e{ }^2}\) (g = acceleration due to gravity) ………..(ii)
From equations (i) and (ii),
F = mg
The work done in raising the body to a height ‘h’
W = F x S (∵ s = h) = mgh
Because work done is same as the energy. Therefore, at a height ‘h’ the potential energy of the object is,
Potential Energy (P.E.) = mgh

Question 2.
Define kinetic energy. Obtain an expression for it.
Answer:
Kinetic Energy:
The energy possessed by a body due to its motion is called kinetic energy.

Expression:
Let us suppose a body of mass m is dropped from a height h and its velocity becomes V.
on reaching the ground level Then –
Initial velocity of the body (u) = 0
Acceleration (a) = g (acceleration due to gravity)
Final velocity = v
Distance (s) = Height (h)
We know that, v² – u² = 2as
v² – 0 = 2gh
v² = 2gh
h = \(\frac{v^2}{2 g}\) …………. (i)
As the object comes down, its potential energy decreases and kinetic energy increases. When the body strikes to the ground level, its hoIe potential energy is converted into kinetic energy. According to the law of conservation of energy, Energy can neither be increased nr be decreased.”
Thus, kinetic energy at ground level = Potential energy at height h.
Kineiic Energy = mgh
or K.E. = mg x \(\frac{v^2}{2 g}\) (∵ h = \(\frac{v^2}{2 g}\))
K.E. = \(\frac {1}{2}\) mv²

Question 3.
Define Law of conservation of energy. Give an example of conservation of energy.
Answer:
Law of conservation of energy-According to this law, energy can neither be created nor be destroyed. ¡t can only be transfèrred from one form to another. When the energy is released in any form, the same amount of energy appears in other forms. Thus, total energy of the universe remains constant. Suppose, an object of mass m starts falling from a height h, on the ground level.

(a)EnergyatpointA, PotentialEnergy = mgh
Kinetic Energy = 0
∴ Total energy = mgh + 0 = mgh ……………(i)

(b)Energy at point B:
Suppose the object falls from A to B at a distance s, then its height from ground level will be (h-S).
∴ Potential energy = mg (h-s)
and v²-u² = 2gs
v² = 2gs [∵ u = 0]
Kinetic Energy = \(\frac {1}{2}\) mv² = \(\frac {1}{2}\)m x 2gs = mgs
Total Energy = mg (h-s) + mgh = mgs – mgs + mgs = mgh …………(2)

(c) Energy at point C; v²-u² = 2gh
v² = 2gh [∵u = 0]
Kinetic Energy = \(\frac {1}{2}\) mv² = \(\frac {1}{2}\) m x 2gh = mgh
and Potential Energy = 0
Total Energy = mgh + 0 = mgh ……………(iii)
in this way we observe from eQuestion (i), (ii) and (iii) that the energy of the object remains constant at every point. There is potential energy in the object at highest point. When it falls litle downs same part of potential energy is converted into kinetic energy and on ground level whole potential energy is converted into kinetic energy.

Practical Work

Experiment 1.
Describe by an experiment that the wark done by a force can either be positive or negative.

Procedure:
A child is pulling a toy car parallel to the ground as shown in figure. The child has exerted a force in the direction of displacement of car. In this situation, the work done will be equal to the product of the force and displacement. In this situation the work done by the force is taken as positive. Consider a situation in which an object is being displaced by the action of forces and we identit one of the forces, F acting Opposite to the direction of the displacement s, thus, the angle between the two directions is 1800.

In such a situation, the work ‘ done by the force F is taken as negative and denoted by the minus sign. The work done by the force is F x (-s) or (-F x s). When the force acts opposite to the direction of the displacement, the work done is negative. When the force acts in the direction ofdisplacernen, the work done is positive.

Experimenf 2.
Describe by an activity in which both positive and negative forces are working.

Procedure:
When an object is lifted up, both positive and negative forces work, because the force applied by us, displaces the object upward and called positive force, while the force of gravity applied by earth pulls the object downward which is called negative force.

Experiment 3.
Describe by an experiment that the object at more height has more energy.

Procedure:
(1) Take a heavy ball. Drop it on a thick bed of sand. A wet bed of sand would be better. Drop the ball on the sand bed from height of about 25 cm. The ball creates a depression.
(2) Repeat this activity from heights of 50 cm, I m and 1.5 m.
(3) Ensure that all the depressions are distinctly visible.
(4) Mark the depressions to indicate the height from which the ball was dropped.
(5) Compare their depths.

We will observe that when the ball was dropped from the height of 1.5 m, the depression was the deepest; which proves that the object at more height has more energy which makes the deepest depression.

Expereiient 4.
Describe by an experiment that the kinetic energy of an object increases by increasing its mass.

Procedure:
(1) Set up the apparatus as shown in figure
(2) Place a wooden block of known mass in front of the trolley at a convenient fixed distance.
(3) Place a known mass on the pan so that the trolley starts moving.
(4) The trolley moves forward and hits the wooden block and displaces the block.
(5) Note down the displacement of the block. It is, clear that the work is done on the block by the trolley as the block has gained energy.
(6) Repeat this activity by increasing the mass on the pan.

You will observe that the displacement will increase with the increase in mass, which proves that the kinetic energy increases by increasing the mass.

Quick Review of the Chapter

1. What is required for doing a work?
(A) displacement in object
(B) force should be applied on the object
(C) both (A) and (B)
(D) no displacement in object
Answer:
(C) both (A) and (B)

2. What type of energy is there inside a body kept at height?
(A) potential
(B) kinetic
(C) both (A) and (B)
(D) no relation with energy
Answer:
(A) potential

3. The device that converts the electrical energy In heat energy:
(A) Electrical iron
(B) Electrical bulb
(C) Radio
(D) Electrical motor
Answer:
(A) Electrical iron

4. Which type of energy is there in a flying bird?
(A) potential
(B) kinetic
(C) both (A) and (B)
(D) neither of the two
Answer:
(C) both (A) and (B)

5. Rado transfer the electrical enegry in:
(A) light energy
(B) sound energy
(C) mechanical energy
(D) heat energy
Answer:
(B) sound energy

6. Which formula is correct for work?
(A) W = \(\frac {F}{s}\)
(B) W = \(\frac {s}{F}\)
(C) W= Fs
(D) W = \(\frac {1}{Fs}\)
Answer:
(C) W= Fs

7. The unit of force Is:
(A) Newton
(B) Newton metre
(C) Joule
(D) both (B) and (C)
Answer:
(A) Newton

8. If 5n force acts on an object, then displacement is 2m, what will be the work done?
(A) lONm
(B) IOJ
(C) lOJm
(D) both(A)and(B)
Answer:
(D) both (A) and (B)

9. A coolie lifts an object of mass iS kg from the earth to 1.5 m keep it on his head. Calculate the
amount of work done by the coolie.
(A) 22.5J
(B) 2.25 J .
(C) 225J
(D) 225N
Answer:
(C) 225 J

10. The potential energy of an object of mass 1kg kept at the height &f 2m will be:
(A) 9.8J
(B) 19.6J
(C) 29.4 J
(D) 39.2 J
Answer:
(B) 19.6 J

11. Whose unit is Newton metre (Nm)?
(A) work
(B) force
(C) acceleration
(D) power
Answer:
(A) work

12. How many watts are in 1 Kilowatt?
(A) 10³
(B) 10⁴
(C) 10⁵
(D) 10⁶
Answer:
(A) 10³

13. How many joules are in 1 Kilowatt?
(A) 36 lakhs
(B) 36 thousands
(C) 36 hundreds
(D) 36 crores
Answer:
(A) 36 lakhs

14. What is another name of newton metre?
(A) Erg
(B) Coulomb
(C) Joule
(D) Hertz
Answer:
(C) Joule

15. ……….. is vector.
(A) potential energy
(B) kinetic energy
(C) work
(D) none of these
Answer:
(D) none of these

16. A man stands for 10 minutes by carrying a weight of 20 kg the work done s ill be:
(A) 200joule
(B) onejoule
(C) zero
(D) 400joule
Answer:
(C) zero

17. The unit of energy is:
(A) Nm
(B) Joule
(C) both (A) and (B)
(D) no unit
Answer:
(C) both (A) and (B)

18. The example of kinetic energy is not:
(A) stone kept on mountain
(B) revolving wheel
(C) blowing air
(D) bullet shot out of a gun
Answer:
(A) stone kept on mountain

19. The example of potential energy is not :
(A) an arrow kept in the bow
(B) a stone on a mountain
(C) falling coconut
(D) a bullet in a gun
Answer:
(C) falling coconut

20. An object of 10 kg mass is carried to a height of 6 m. Calculate the energy of the object. (g = 9.8 mc²)
(A) 98 J
(B) 58.8 J
(C) 588 J
(D) 5880 J
Answer:
(C) 588 J

21. The law of conservation of mass is:
(A) all works require energy
(B) energy can be produced
(C) energy can be destroyed
(D) energy neither can be produced nor destroyed
Answer:
(D) energy neither can be produced nor destroyed

22. Which statement is not correct?
(A) Potential energy + kinetic energy constant
(B) Kinetic energy + potential energy = mechanical energy
(C) As much decrease is there in potential energy at a point so is in kinetic energy
(D) As much decrease is there in potential energy so much increase takes place in kinetic energy.
Answer:
(C) As much decrease is there in potential energy at a point so is in kinetic energy

23. Which formula is correct?
(A) P = W x t
(B) P = \(\frac {W}{t}\)
(C) P = \(\frac {t}{W}\)
(D) P = \(\frac{1}{W \times t}\)
Answer:
(B) P = \(\frac {W}{t}\)

24. What is the unit of power?
(A) Joule
(B) Nm
(C) erg
(D) Watt
Answer:
(D) Watt

25. How much energy will be consumed by a person of 600 newton weight for climbing a height of 10m?
(A) 60 joule
(B) 600 jouie
(C) ó000joule
(D) 588 joule
Answer:
(C) 6000 joule

26. When will be the minimum amount of potential energy in your body ? When you:
(A) are standing
(B) are sitting in a chair
(C) ire lying on the earth
(D) are sitting on the earth
Answer:
(C) are lying on the earth

27. When ¡s work not done?
(A) on fixing a nail in a wood
(B) on sliding a box on the floor
(C) when there is no constituent of parallel force in the direction of motion
(D) a weight hanging on a peg
Answer:
(C) when there is no constituent of parallel force in the direction of motion

28.
10 seconds are taken to fetch a bucket of 5 kg mass from a well of 10 m depth. The power used in the power will be:
(A) 5ONm
(B) 50)
(C) 50 W
(D) 500 W
Answer:
(C) 50 W

29. How much energy will be consumed by 5 fans of 100 watt each in 4 hours?
(A) 20 kwh
(B) 10 kwh
(C) 2 kwh
(D) 1 kwh
Answer:
(C)2 kwh

30. The rate of doing work is called:
(A) Power
(B) Force
(C) Energy
(D) None of these
Answer:
(A) Power

31. What is the momentum of an object of mass m, moving with a velocity u?
(A) (mυ)²
(B) mυ²
(C) \(\frac {1}{2}\) mυ²
(D) mυ²
Answer:
(C) \(\frac {1}{2}\) mυ²

Haryana State Board HBSE 9th Class Science Important Questions Chapter 10 Gravitation Important Questions and Answers.

Haryana Board 9th Class Science Important Questions Chapter 10 Gravitation

Very Short-Answer Type Questions

Question 1.
What is meant by gravitation?
Answer:
Everybody on earth attracts each other. Such type force of attraction between bodies is called gravitation.

Question 2.
Who discovered the gravitational force firstly?
Answer:
Sir Isaac Newton.

Question 3.
In which direction the gravitational force between two objects works?
Answer:
The gravitational force between two objects works in the direction of a line joining the centre of their masses.

Question 4.
Which force is responsible for the existence of our solar system?
Answer:
Gravitational force is responsible for our solar system.

Question 5.
What ‘G’ indicates?
Answer:
‘G’ indicates gravitational constant.

Question 6.
What is the value of ‘G’ ? ’
Answer:
VMtte of‘G’ is 6.673 x 10¹¹ Nm²/kg²

Question 7.
How much is the mass of earth ?
Answer:
Mass of earth (M_e) = 6 x 10²⁴ kg (approx.).

Question 8.
How much is the radius of earth ?
Answer:
Radius of earth (R_e) = 6.4 x 1o⁶m.

Question 9.
At which part of earth, the value of g is maximum and minimum?
Answer:
The value of g is maximum on poles of earth and minimum on the equator. ‘

Question 10.
Write the formula for the force of attraction between two objects of masses m₁ and m₂ respectively kept at a distance of R.
Answer:
F = \(\frac{\mathrm{Gm}_1 \mathrm{~m}_2}{\mathrm{R}^2}\)

Question 11.
What is acceleration due to gravity (g) ?
Answer:
The acceleration by which earth attracts other object towards its centre is called acceleration due to gravity.

Question 12.
Does the acceleration of an object falling towards earth depend upon its mass ?
Answer:
No, the acceleration of an object falling towards earth does not depend upon its mass.

Question 13.
What will be the force of attraction between two objects if the distance between them becomes twice ?
Answer:
Force of attraction will become one-fourth.

Question 14.
What will be the weight of an object on moon in comparison to earth ?
Answer:
\(\frac {1}{6}\) times.

Question 15.
What is centripetal acceleration ?
Answer:
When an object moves on a circular track’ ah acceleration is produced due to change in velocity, which is called centripetal acceleration.

Question 16.
What is centripetal force ?
Answer:
The force which produces centripetal acceleration is called centripetal force. It is always directed towards centre. That is, F = \(\frac{\mathrm{mv}^2}{\mathrm{r}}\)

Question 17.
What ‘g’ indicates ?
Answer:
‘g’ indicates acceleration due to grayity.

Question 18.
What is the value of ‘g’ near the syrfepe of earth ?
Answer:
The value of ‘g’ is 9.8 m/s².

Question 19.
On which place, the value of ‘g’ is zero ?
Answer:
The value of‘g’is zero at the centre of earth.

Question 20.
Write the formula for the relation between ‘g’ and ‘G’
Answer:
g = \(\frac{\mathrm{G} \times \mathrm{M}_{\mathrm{e}}}{\mathrm{R}^2}\)

Question 21.
What are the factors on which the gravitational force depends ?
Answer:
(i) On the mass of objects.
(ii) On the distance between objects.

Question 22.
What is the distance of moon from earth ?
Answer:
60 times of the radius of earth – 384000 km.

Question 23.
If an object is dropped from height A with zero velocity, then how much distance it will cover in one second ?
Answer:
Distance covered, h = \(\frac {1}{2}\) gt²

Question 24.
Whose value, out of ‘g’ and ‘G’ is constant and whose not ?
Answer:
The value of ‘G’ is constant at every place on earth, but value of ‘g’ is more on poles and less on equators.

Question 25.
How much time does the earth take to move around the sun ?
Answer:
The earth takes 365 \(\frac {1}{4}\) days to move around the sun.

Question 26.
How much time does the moon take to move around the earth ?
Answer:
The moon takes 27 days 8 hours to move around the earth.

Question 27.
What is meant by mass ? Write its unit.
Answer:
Mass is the quantity of matter contained in it. Its unit is kilogram.

Question 28.
What is meant by weight ? What is its measurement unit ?
Answer:
The force by which earth attracts an object towards itself is called the weight. Its measurement unit is Newton.

Question 29.
What is meant by weight lessness ?
Answer:
The state of body when gravity of planet (earth) stops acting, the person in spaceship is in the state of weightlessness.

Question 30.
What is meant by centre of mass ?
Answer:
The centre of mass is that point at which whole mass of object is directed.

Question 31.
What is meant by centre of gravity ?
Answer:
The centre of gravity is that point of the object at which the whole force of gravity works.

Question 32.
Where is the centre of gravity of objects having regular shape ?
Answer:
The centre of gravity of die objects having regular shape and equal density lies on geometrical centre.

Question 33.
What will happen if the mass and acceleration of two objects become equal ?
Answer:
If the mass and acceleration of two objects become equal, then they will appear to move towards ‘ each other.

Question 34.
What is meant by the force of gravity ?
Answer:
The force between earth and an object is called the force of gravity.

Question 35.
Which balance is used to measure weight ?
Answer:
Spring balance is used to measure weight.

Question 36.
Which balance is used to measure mass ?
Answer:
Physical balance is used to measure mass.

Question 37.
Why is the weight of the object less on the moon in comparison to the earth ?
Answer:
Because the acceleration due to gravity on the ftibon is less than that on the earth.

Question 38.
Two stones of masses 25 kg and 2 kg are dropped at the same time from the top of a building. Which stone will reach first on earth ?
Answer:
The acceleration due to gravity does not depend upon the mass of the object. So both stones will reach on the earth in same time.

Question 39.
There is gravitational force between two objects kept on table. Why they don’t move towards each-other even in the presence of this force ?
Answer:
The gravitational force between two objects is very weak so that they do not move.

Question 40.
The earth attracts an iron pin downward with gravitational force, but the magnet attracts the iron pin upwards against the direction of attraction of earth, why ?
Answer:
Because attractive force applied by magnet on iron pin is more than the gravitational force on pin.

Question 41.
Where the gravitational force will be more-between two objects on earth or between object and earth ?
Answer:
The gravitational force between object and earth is more.

Question 42.
Where is the weight of the object zero ?
Answer:
The weight of the object is zero at the centre of earth.

Question 43.
What is the relation among u, v, g and t ?
Answer:
v = u + gt

Question 44.
What is the sign of ‘g’ according to Cartesian Coordinate system ?
Answer:
‘g’ is always taken as negative.

Question 45.
What is meant by projectile range ?
Answer:
The maximum horizontal distance covered by projectile is called projectile range.

Question 46.
What is the angle between velocity and acceleration at the highest point of projectile ?
Answer:
Right angle (90°).

Question 47.
How far is the sun from the earth ?
Answer:
1.5 x 10¹¹ metres.

Question 48.
What is meant by thrust ?
Answer:
The force acting perpendicular to the surface of object is called thrust.

Question 49.
Give an example of thrust in daily life.
Answer:
When we press a pin on drawing board, the force applied by our thumb acts in perpendicular direction on board. Thus, it is thrust.

Question 50.
What is pressure ? What is its SI unit ?
Answer:
The thrust per unit area is called pressure. That is pressure  Its SI unit is Pascal (Pa).

Question 51.
What is the SI unit of thrust ? Africa
Answer:
Newton (N).

Question 52.
In regard of which scientist, the SI unit of pressure is Pascal (Pa) ?
Answer:
In honour of scientist Blaise Pascal.

Question 53.
What is the bigger unit of pressure ?
Answer:
Kilopascal (k Pa).

Question 54.
Why cutting, tearing and grooving apparatus are always sharp ?
Answer:
The cutting, tearing and grooving apparatus are sharp so that thrust affects minimum area to increase pressure and the object can be cut, tear or groove easily.

Question 55.
When is the pressure of man more -sitting on ground or standing at one place and why ?
Answer:
The pressure of man is more when standing at one place because the area in standing position is less than that in sitting position at one place.

Question 56.
What is the effect of depth on liquid pressure ?
Answer:
The liquid pressure increases with depth.,

Question 57.
Why do the egg floats in salty water ?
Answer:
The density of water increases by adding salt in it, due to that buoyant force of water increases and the egg floats.

Question 58.
In which stage, the object floats ?
Answer:
If the weight of the body is equal to the weight of fluid displaced, then the object floats on the surface of fluid.

Question 59.
Write the name of two devices that work on Archimedes’ principle.
Answer:
(i) Ship and
(ii) submarine.

Question 60.
Which device is used to measure the purity of the milk and what is its principle ?
Answer:
The lactometer is used to measure the purity of the milk which works on Archimedes’ principle.

Question 61.
Write the name and principle of that device which is used to measure the density of liquids.
Answer:
Hydrometer, which works on Archimedes’ principle.

Question 62.
What is the mass of unit volume called ?
Answer:
Density.

Question 63.
What is the SI unit of density ?
Answer:
Kilogram per metre cube (kg m^-3).

Short Answer Type Questions

Question 1.
If a piece of stone is allowed to fall freely from a certain height, then what will be the changes in velocity ?
Answer:
The following are the changes :
(1) The initial velocity of stone is zero and it increases at coming down.
(2) The stone nearest to earth has maximum velocity.
(3) The velocity of stone becomes zero after striking the ground. –

Question 2.
What is gravitation ? In which direction it works ?
Answer:
Everybody of universe attracts other body towards itself. This attraction between two bodies is gravitation. This attraction between two bodies works along the line joining the centres.

Question 3.
Prove that acceleration produced in the object dropped towards the earth does not depends upon its mass.
Answer:
If an object of mass, m is dropped from the centre of earth at a distance of R, then the force exerted by the earth on object,
F = \(\frac{\mathrm{GM}_{\mathrm{e}} \mathrm{m}}{\mathrm{R}^2}\)
Where, M_e = mass of earth, G = gravitation constant
∴ Acceleration produced in the object = \(\frac {F}{m}\) (F = ma; a = \(\frac {F}{m}\))
= \(\frac{\frac{\mathrm{GM}_{\mathrm{e}} \mathrm{m}}{\mathrm{R}^2}}{\mathrm{~m}}\) = \(\frac{\mathrm{GM}_{\mathrm{e}} \mathrm{m}}{\mathrm{R}^2} \times \frac{1}{\mathrm{~m}}=\frac{\mathrm{GM}_{\mathrm{e}}}{\mathrm{R}^2}\)
∴ The acceleration produced in an object does not depend upon the mass of dropped object.

Question 4.
What is Newton’s third law of motion ? Is this law applicable on gravitational force ? Explain.
Answer:
According to Newton’s third law, “To every action, there is equal and opposite reaction.” For example, we act on ball when we throw it on wall and ball comes back by the reaction of wall. Thus, an object A exerts a force on object B, then object B is also exerts equal and opposite force on A. This fact is also true for gravitational force. When a stone falls on earth, it happens due to the force of gravity of the earth on stone. In fact, the piece of stone, attracts the earth towards itself with equal force of gravity. But the mass of stone is less than that of the earth so the force exerted by the stone on the earth is less. Therefore the stone seems to attracted towards earth.

Question 5.
Discuss the motion of the object thrown upward.
Answer:
When a body is thrown upward, the earth attracts that body continuously towards itself. Therefore, the gravitational force works in opposite direction of motion and the body moves slowly. The speed reduces at a rate of 9.8 ms-2 in every second. At last when the body reaches at highest point, the speed becomes zero. The body again starts falling towards earth with an acceleration of 9.8 ms-2.

Question 6.
Find the unit of ‘G’
Answer:
‘G’ is the ratio of force (F) and \(\frac{M_1 M_2}{R^2}\) Therefore, its unit depends upon the units offorce, mass and distance. If the mass is taken in kilogram, distance in metre and time in second, then the uqit offorce is newton (N).
Unit of G = \(\frac{M_1 M_2}{R^2}\) = Nm²/kg²

Question 7.
Why is G called universal constant ?
Answer:
We know that F = G \(\frac{m_1 m_2}{R^2}\)
‘G’ is constant among diem. The value of ‘G’ does not depend upon the Value of mj, m2 or R. Its value does not depend upon that how, when and where the force is measured. The value of‘G’ remains consant for any two bodies in universe. The ratio of F and \(\frac{m_1 m_2}{R^2}\) is equal to G which is equal for any two bodies. That is why, G is called universal constant.

Question 8.
What is the difference between ‘g’ and ‘G’ ?
Answer:
The difference between ‘g’ and ‘G’ is as follows:

g:	G:
1. It indicates acceleration due to gravity.	1. It indicates gravitational constant.
2. Its value vary from place to place.	2. Its value is same everywhere. Therefore, it is called universal constant.
3. Its value on earth is 9.8 ms-2.	3. Its value is 6.673 x 10-11 Nm2 kg-2.
4. It is always negative.	4. It is always positive.

Question 9.
Prove that the bodies of different masses when dropped together from the same height, strikes in same time (assume, air resistance is negligible).
S0lution:
Suppose two objects of different masses were dropped together from same height h,
In this state s = h, u = 0
According to formula s = ut + \(\frac {1}{2}\) gt²
h = 0 x t + \(\frac {1}{2}\) gt²
Or h = \(\frac {1}{2}\) gt²
Or 2h = gt²
Or gt² = 2h
t² = \(\frac {2h}{g}\)
Or t = \(\sqrt{\frac{2 h}{g}}\)
It is clear from the equation that the time taken by objects does not depend upon masses. Thus, both objects fall in same time on earth.

Question 10.
What is meant by vertical direction of earth?
Answer:
If we suppose the earth as a ball of uniform density, then its centre of mass will be at its centre. Thus, the force of attraction of the earth on a body works in the direction of its (earth) centre. This is the direction which we call vertical direction.

Question 11.
Which are equations related to the freely falling bodies?
Solution:
(i) v = u + gt
(ii) v² – u² = 2gs
(iii) s = ut + \(\frac {1}{2}\) gt²
Here,
u = initial velocity
y = final velocity
g = acceleration due to gravity
s = distance or height
t = time

Question 12.
What is meant by weight ? Write the formula for weight.
Answer:
The force of attraction applied by earth on an object is called its weight. if earth produces an acceleration ‘g’ on an object of mass, m then, the force of artraction applied by earth on object, F = mg
But, the force of attraction applied by the earth on object (F) = Weight of object (W) = W = mg

Question 13.
Find a formula to compare the weight of a body on earth and on any other heavenly body.
Solution:
Suppose, mass of the object = m
Mass of the earth = M_e
Radius of earth = R_e
The attractive force applied by earth on object, F_e = \(\frac{\mathrm{GM}_{\mathrm{e}} \mathrm{m}}{\mathrm{R}_{\mathrm{e}}{ }^2}\) ………..(i)
Suppose, mass of hçavenly body = M_m
Radius of heavenly body = R_m
The force of attraction applied by other heavenly body on object
F_m = \(\mathrm{G} \frac{\mathrm{M}_{\mathrm{m}} \times \mathrm{m}}{\mathrm{R}_{\mathrm{m}}^2}\) …………..(ii)

Dividing eq (ii) by eq (1)
\(\frac{\mathrm{F}_{\mathrm{m}}}{\mathrm{F}_{\mathrm{e}}}=\frac{\mathrm{M}_{\mathrm{m}}}{\mathrm{M}_{\mathrm{e}}} \times\left(\frac{\mathrm{R}_{\mathrm{e}}}{\mathrm{R}_{\mathrm{m}}}\right)^2\)

Question 14.
Find the relation between acceleration due to gravity (g) and universal gravitational constant (G).
Answer:
Suppose an object of mass m is kept at a distance of R from the centre of the earth. If M is the mass of the earth, then the force applied by earth on that object:
F = \(\mathrm{G} \frac{\mathrm{Mm}}{\mathrm{R}^2}\) ………..(i)
The force by which the earth attracts the object towards its centre, is cal led weight. It is also denoted by’ F’.
F = mass (m) x acceleration due to gravity (g)
or F = mg ……….(ii)
From equations (i) and (ii) mg = \(\mathrm{G} \frac{\mathrm{Mm}}{\mathrm{R}^2}\)
Or g = \(\frac{\mathrm{GM}}{\mathrm{R}^2}\)
This is the required relation. The value of’g’ can be found with the help of this.

Question 15.
What is mass ? What is its measurement unit ? WrIte the law to measure mass.
Answer:
Mass: The quantity of matter contained in an object is called its mass. It is a scalar and constant quantity.
The unit of mass is kilogram. It is found by physical balance.

Law to measure mass:
Suppose we have two objects of masses m₁ and m₂, kept at the same distance from the centre of the earth, then the force of attraction between the earth and m₁:
F₁ = R₂
Here, M_e = mass of earth and R = distance of mass m₁ from the centre of the earth.
Like this, the force of attraction between the earth and m₂
F₁ = \(\frac{\mathrm{GM}_{\mathrm{e}} \mathrm{m}_1}{\mathrm{R}^2}\)
Here, M_e = mass of earth and R = distance of mass m₁ from the centre of the earth.
Like this, the force of attraction between the earth and m₂
F₂ = \(\frac{\mathrm{GM}_{\mathrm{e}} \mathrm{m}_2}{\mathrm{R}^2}\)
1f both the forces are same, then F₁ = F₂
\(\frac{\mathrm{GM}_{\mathrm{e}} \mathrm{m}_1}{\mathrm{R}^2}=\frac{\mathrm{GM}_{\mathrm{e}} \mathrm{m}_2}{\mathrm{R}^2}\)
∴ m₁ = m₁
Thus, if two forces are equal then the masses of two objects will be equal and parts of physical balance will be equal.

Question 16.
Define projectile and path of projection and give some examples of projection motion.
Answer:
Projectile:
A body thrown in horizontal direction is called projectile.

Path of projection:
The curved path travelled by projectile is called path of projection.

The examples of projection motion are following:
(1) The path of a body dropped from aeroplane, i.e., a ball falling from a building of 80m high is shown in figure.
(2) The path of a bullet fired from gun.
(3) The path of sphere thrown by player.

Question 17.
Why do astronauts feel weightlessness in spaceship?
Answer:
When the astronauts sitting in spaceship move around the earth, the gravitational force between the earth and spaceship is balanced by the force used to move around the earth, due to that the astronauts feel weightlessness. The value of acceleration due to gravity becomes zero in spaceship.

Question 18.
Generally, if the cotton ball and stone of same size are allow ed to fall from a certain height, then which one will strike the surface of earth first? What Galello discussed about this fact?
Answer:
Generally, the piece of stone reaches first on the surface of earth in comparison to cotton. But first of all Galelio told that the air resistance becomes zero, cotton ball and piece of stone will reach in same time on the surface of earth with equal acceleration. According to Galelio. “the objects the acceleration of falling on the acceleration of the earth does not depend upon their masses.”

Question 19.
How does acceleration due to gravity change at any place (i) due to height, (ii) due to the shape of the earth?
Answer:
In the following way the acceleration due to gravity changes at any place:
(i) Due to height: The value of ‘g’ is less on the mountains situated at some height on earth surface, whereas it ¡s more on plain surface.
∴ \(\frac{W_h}{W}=\frac{g_h}{g}=\frac{R^2}{(R+h)^2}\)
Like this, the value of ‘g’ goes on decreasing by increasing height.

(ii) Due to the shape of earth: The earth is not completely round like a ball, but it is convexed at the equator line and concaved at the polar line. There is a difference of 22 km between the radius of the equator and polar line of the earth. That’s why
the value of’g’ is more on poles and less on equators.
∴ g = \(\frac{\mathrm{GM}}{\mathrm{R}^2}\) (Where, G and M are constant.)
∴ g ∝ \(\frac{1}{R^2}\)

Question 20.
“The moon falls towards the earth.” What does it mean ? Why does it not fall on the surface of the earth?
Answer:
The moon falls towards the earth means that the earth attracts the moon towards itself due to its gravitational force. But, moon moves around the earth in a circular path and does not fall, because the velocity of the object moving on a circular path changes at every point. The change in velocity or acceleration is due to the change in the direction of motion of the object. The centripetal force which produces this acceleration maintains the body to move in circle, which is always directed towards the centre.

Question 21.
The earth attracts the apple, does the apple also attract the earth ? If yes, then why the earth does not move towards the apple?
Answer:
Definitely the apple attracts the earth towards itself, but the mass ofapple is negligible in comparison to earth so the earth does not move towards apple.

Question 22.
What are Kepler’s three laws of motion?
Answer:
Kepler’s is three laws of motion are following:
(i) The orbit of a planet is an ellipse with the sun at one of the foci. As the position of sun is shown by in the figure.
(2) The line joining the planet and the sun sweep equal area in equal intervals of time. Thus, if the time of travel from A to B is same as that from C to D, then the areas OAB and OCD are equal.
(3) The cube of the mean distance of a planet from the sun is proportional to the square of its orbital period, T, or constant. It is important to know that Kepler could not give a theory to explain the motion ofplanets. It was Newton who showed that the cause of the planetory motion is the gravitational force that the sun exerts on them.

Question 23.
Why are the tyres of buses or trucks wider than that of cars?
Answer:
The thurst on buses or trucks is more than that on cars. If their tyres are made less wider than the tyres of cars, the pressure on them will increase and they will sink ¡n earth. Therefore, the tyres of buses or trucks are made wider, so that the area will increase and pressure on earth decrease.

Question 24.
The camel can walk in desert easily, but ¡t is difficult for horse to walk, why?
Answer:
The area of feet of camel is more than that of horse. So the affected area is more and pressure decreases. The camel can walk easily in desert due to less pressure. But the area of feet of horse is less, and the pressure increases. Due to large pressure, it is difficult to walk by horse in desert.

Question 25.
What is buoyant force? [low is it measured?
Answer:
When a body is immersed in a fluid, an upward force works on the body which is called buoyant force. Measurement of Buoyant Force: Take a metal’s sphere. Hang it on spring balance and note its weight. Let its weight is W1 gm. Now put some water in a beaker and take the sphere in the beaker slowly. You will see that the weight of sphere seems decreasing when put in water slowly, which is indicated by spring balance. Note the indicator of spring balance when the solid sphere immersed completely in water.
Let it is W₂ gm.
The difference between two weights will be the buoyant force of water.
Buoyant force = weight of sphere in air – weight of sphere in water.
= (W₁ – W₂)gm

Question 26.
What is the reason that, an iron needle sinks in water, but a ship made up of iron floats in water?
Answer:
The iron needle sinks in water, but a ship made of iron floats in water because weight of water displaced by needle is less than the weight of needle. Due to heavy weight, the needle sinks in water. But the weight of water displaced by ship is more than the weight of ship and it floats in water.

Question 27.
Why is it easy to swim in sea water than river?
Answer:
It is easy to swim in sea water than river because the density of sea water is more than the density of river water. Thus, the sea water due to being heavy, applies larger buoyant force on the body of person, duc to this reason it is easy to swim in sea water.

Question 28.
What is density ? What is its SI unit ? What is its importance?
Answer:
The mass per unit volume of a body is called density. Its SI unit is kilogram per metre cube. The density of the substance always remain same in certain circumstances. The density of gold ¡s 19300 kg m^-3 and the density of water is 1000 kg m^-3.
Importance: The density of the sample of any substance helps in the measurement of its purity.

Question 29.
What is relative density ? What is the condition of sink or float in water on the basis of it?
Answer:
The ratio of density of substance and density of water is called relative density of the body. Thus density of substance

∴Relative density is a ratio, so, it has no unit.
The relative density ofgold is 19.3. If the relative density of any solid or liquid is more than I, it will sink in water, if it is less than 1, it will float in water.

Question 30.
Why the ice floats on water?
Answer:
The ice floats on water because the density of ice is less than the density of water. when a piece of the ice is put in the water, then its weight is less than the weight of water displaced by it.

Question 31.
Define Archimedes’ principle and explain it. What arc uses of this principle? Or Define Archimedes’ Principle. Write Iwo applications ofArchimedes’ Principle.
Answer:
Statement of Archimedes’ principle: When a body is immersed fully or partially ¡n a fluid, it expirences an upward force that is equal to the weight of the fluid displaced by it.

Explanation:
When a solid is immersed in a fluid, the fluid pushes it upwards by its buoyant force, and its wekht decreases, because buoyant force is equal to the weight of water displaced by the solid. So the decrease in weight of solid when immersed ¡n fluid is equal to the weight of the water displaced.

Uses of Archimedes’ principie in daily life:
(I) It is used in designing of ships and submarines.
(2) The lactometer, which is used to determine the purity of milk, is based on this principle. .
(3) The hydrometer which is used for determining density of liquid, is also based on this principle.

Question 32.
What happens to the gravitational force between two objects If:
(i) the distance between the objects ¡s one-third (1/3)?
(ii) the masses of both the objects are halfed (1/2)?
Answer:
(i) As we know that gravitational force between two objects is inversely proportional the square of the distance between them. So, if the distance between them is then the gravitational force between them will be 9 times.
(ii) As the gravitational force between two objects is proportional to the product of masses of two objects. So, if the masses of two objects are halfed (1/2) then the gravitational force between them will be one tourth (1/4).

Numerical Questions

Question 1.
A bullet is fired with a velocity of 25 ms1 in horizontal direction. How much distant it will fall in first two seconds?
Solution:
Vertical distance is independent to horizontal velocity.
∴ Initial velocity (u) = 0
Acceleration due to gravity (g) = 9.8 ms^-2
Time (t) = 2s
Distance (s) = ?
We know that
s = ut + \(\frac {1}{2}\) gt²
= 0 x 2 +\(\frac {1}{2}\) x 9.8 x (2)²
= 19.6 m

Question 2.
Find the weight of an object of mass 5 kg.
Solution:
Mass of the object (m₁) = 35 kg
Acceleration due to gravity (g) = 9.8 ms^-2
Weight of the object (W) = ?
We know that, W = m x g = 5 x 9.8 = 49 N

Question 3.
If the mass of you and your friend is 35 kg, and the distance between you and your friend is 1 m, then what will be the force of attraction between two?
Solution:
Here,
Mass(m₁) = 35kg
Ma.ss(m₂) = 35kg
Distance(r) = 1 m
Gravitational constant (G) = 6.67 x 10^-11 Nm² kg^-2
Force of attraction (F) = ?
We know that, Force of attraction, (F) = \(\frac{\mathrm{Gm}_1 \mathrm{~m}_2}{\mathrm{r}^2}\)
= \(\frac{6.67 \times 10^{-11} \times 35 \times 35}{(1)^2}\)
= 8.17 x 10^-8 N Ans

Question 4.
FInd the weight of an object of mass 10 kg on the surface of that planet whose mass is two times and radius Is three times that of earth.
Solution:
For planet, M = 2M_e and R = 3 R_e
∴ g₁ = \(\frac{\mathrm{G}\left(2 \mathrm{M}_{\mathrm{e}}\right)}{\left(3 \mathrm{R}_{\mathrm{e}}\right)^2}=\frac{2 \mathrm{GM}_{\mathrm{e}}}{9 \mathrm{R}_{\mathrm{e}}^2}\)
= \(\frac {2}{9}\) g
= \(\frac {2}{9}\) x 9.8 = \(\frac {19.6}{9}\)m^-2 [∵ g = 9.8 m^-2]
∴ Weight of the object of 10 kg on the planet (W) = m x g₁
= 10 x \(\frac {19.6}{9}\) = \(\frac {19.6}{9}\) = 21.78 N

Question 5.
The weight of an object is 49 N, what will be its mass?
Solution:
Weight of object (W) = 49 N
Acceleration due to gravity (g) = 9.8 ms^-2
Weight = mass x acceleration due to gravity
W = mg
49 = m x 9.8
m = \(\frac {49}{9.8}\) = 5 kg

Question 6.
A car fall off a ledge and drops to the ground in 0.5g. Let g = 10 ms^-2
(i) What is the speed of car on striking the ground?
(ii) What ¡s its average speed during \(\frac {1}{2}\) s?
(iii) How high is the ledge from the ground?
Solution:
Time (t) = \(\frac {1}{2}\) s
Initial velocity (u) = 0 ms^-1
Acceleration due to gravity (g) = 10 ms^-2
Acceleration of car (a) = + 10 ms^-2 (downward)
(i) Speed (v) = at
v = 10 ms^-2 x \(\frac {1}{2}\) s = 5 ms^-1

(ii) Average speed = \(\frac {u + v}{2}\) = \(\frac{\left(0 \mathrm{~ms}^{-1}+5 \mathrm{~ms}^{-1}\right)}{2}\) = 2.5 ms^-1

(iii) Distance travelled, s = \(\frac {1}{2}\) at²
= \(\frac {1}{2}\) x 10 ms^-2 x (1/2s)²
= \(\frac {1}{2}\) x 10 ms^-2x (1/4s)² = 1.25 m
Thus
(i) its speed on striking the ground = 5 ms^-1
(ii) its average speed during the \(\frac {1}{2}\) s = 2.5 ms^-1
(iii Height of the ledge from the ground = 1.25 m

Question 7.
A stone ¡s dropped from the edge of the roof:
(i) how long time does It take to fall 4.9 m?
(ii) what is the speed of stone at that time?
(iii) how fast does It move at the end of 1.9 m?
(iv) what is the acceleration after Is and after 2s?
Solution:
(i) Initial velocity of stone (u) = 0
The distance covered by the stone (s) = 4.9 m
g = 9.8 ms^-2
Time, t = ?
Now, S = ut + gt²
4.9 = 0 x t +\(\frac {1}{2}\) x 9.8 x t²
Or 4.9 = 0 + 4.9 t²
Or 4.9 t² = 4.9
Or t² = \(\frac {4.9}{4.9}\) = 1s

(ii) Suppose the speed of stone at that time = v
Now, v = u + gt
v = 0 + 9.8 x 1
v = 0 + 9.8 = 9.8 ms^-1

(iii) initial velocity of stone (u) = 0
The distance covered by the stone (s) = 79 m
g = 9.8 mr^-2, v = ?

Now, v² – u² = 2gs
v² – (0)² = 2 x 9.8 x 7.9
v² – 0 = 154.84
v = 154.84
v = \(\sqrt{154.84}\) = 12.44 ms^-1

(iv) Because the body is faLling freely under the action of gravity.
∴ Acceleration of the body after 1 s = 9.8 ms^-2
Acceleration of the body after 2 s = 9.8 ms^-2

Question 8.
A ball is thrown up vertically upto a height of 100 m, find its initiai speed.
Solution:
Here,
Initial speed (u) = ?
Final speed (v) = 0
Distance (s) = 100m
Acceleration due to gravity (g) = -9.8 ms^-2
Weknowthat, v² – u² = 2gs
0² – u² = 2 x (-9.8) x 100
– u² = – 1960
u = \(\sqrt{1960}\) = 44.2 ms^-1 Ans

Question 9.
What will be the height of building Ifa piece of stone takes 4 seconds when dropped freely from the roof of a building?
Solution:
Here, Initial speed (u) = 0
Time(t) = 4s
Height or distance (s) = ?
Acceleration due to gravity (g) = 9.8 ms²
We know that, s = ut + \(\frac {1}{2}\) gt²
= 0 x 4 + \(\frac {1}{2}\) x 9.8 x (4)²
= \(\frac {1}{2}\) x 9.8 x 4 x 4 = 78.4 m

Question 10.
The volume of a 500 g sealed tin (or box) is 350 cm³. What is the density of sealed tin ? Will it float or sink in water? What will be the mass of the water displaced by this tin?
Solution:
Mass of tin (m) = 500 g = \(\frac {500}{1000}\) kg = 0.5 kg
Volume of tin = 350 cm³
= \(\frac{350}{100 \times 100 \times 100}\) m³
= 35 x 10^-5 m³
Density of tin = \(\frac{\text { mass }}{\text { volume }}=\frac{0.5}{35 \times 10^{-5}}\) kg m^-3
= \(\frac{5 \times 10^5}{35 \times 10}=\frac{10^4}{7}\) kg m³
= 1.429 x 10³ kg m^-3
We know that the density of water = 1000 kg m^-3
= 10³ kg m^-3

∴ Relative density of tin density of water = \(\frac{1.429 \times 10^3}{10^3}\) = 1.429
Because the relative density of tin (is more than 1). Therefore, tin will sink in the water. Thus, mass of the water displaced wilt be less than that of tin.

Question 11.
The volume of a piece of iron is 20cm3 and mass ¡s 156 g. What is its density?
Solution:
Mass of the iron = 156 g
Volume of the iron = 20 cm³

= \(\frac {156}{20}\) = 7.8g cm^-3.

Do Yourself

(1) Write down the expression for the acceleration experienced by a particle on the surface of moon due to the gravitational force on moon. Find the ratio of this acceleration to that experienced by the saine particle on the surface of the earth. if the acceleration due to gravity on earth is 98 ms² what is the acceleration of a particle on the surface of moon?
Answer:
[(i) a = \(\frac{\mathrm{GM}_{\mathrm{m}}}{\mathrm{R}_{\mathrm{m}}}\) (ii) 0.16 (iii) 1.57 ms^-2]

(2) A particle is thrown up in vertical direction with a velocity of 50 ms. What will be its velocity at highest point? What is the maximum height attained by this particle? How much time will it take to reach at highest point?
Answer:
[(i) v = 0 (ii) 125 m (iii) 5 s]

(3) What will be the force due to gravity on the surface of that planet whose mass and radius, both are
half than that of earth ?
Answer:
[Take g = 9.8 ms2 1 [19.6 ms^-2]

(4) A force of 20 N is applied on an object of weight 9.8 N. Calculate the mass of the object and the
acceleration produced.
Answer:
[Take g = 9.8 ms^-2] [1 kg; 20 ms^-2]

(5) The mass of the earth is 6 x 10²⁴ kg and that of the moon is 7.3 x 1o²² kg. 1f the distance between the
earth and the moon is 3.84 x 10⁵ km, calculate the force exerted by the earth on the moon.
Answer:
[19.8 x 10¹⁹ N]

(6) Calculate the force of attraction acting on person of mass 35 kg on the surface of earth. The mass of the earth is 6 x 10²⁴ kg and radius is 6.4 x 10⁶m.
Answer:
[342 N]

(7) Find the force of attraction between two objects having mass 50 kg and 10 kg and the distance between them is 1 metre.
Answer:
[3.34 x 10^-8 N]

(8) The mass of earth is 6 x kg and mass of moon is 7.4 x 10²² kg. 1f the distance between the earth and the moon is 3.84 x 10⁵ km, find the force exerted by the earth on the moon
Answer:
[G = 6.7 x 10^-11 Nm² kg^-2]
[22.01 x 10²⁰N]

(9) An object is thrown up ¡n vertical direction and attains a height of 10 m. Calculate
(i) the velocity with which the object is thrown up and
(ii) time taken by the object to reach the highest point.
[u = 14 ms^-1 t = 1 .43s]

(10) A boy dropped a stone from the edge of a rock of 49 m high. After is, he dropped second stone. What was the speed of second stone if both stones reached the eanh in same time ?
[ Take g = 9.8 ms^-2]
[12.08 ms^-1]

(11) By which initial velocity, the ball will be thrown up so that it can go upto a height of 40 m.
Answer:
[28 ms^-1] [10 kg]

(12) Find the mass of that object whose weight is 196 N.
Answer:
[Take -9.8 ms^-2] (10 kg]

(13) An aeroplane is flying at a height of 1000 m in horizontal direction with a velocity of 100 ms^-1. A bomb is dropped from it. Calculate:
(i) the time taken by the bomb to reach earth.
(ii) the velocity before striking the ground.
(iii) the distance of target.
Answer:
[(1) 14.28 s ((ii) 172.4 ms^-1 ((iii) 1428.5 m]

(14) The mass of an object ¡s 10 kg. What will be its weight on the earth?
Answer:
[98 N]

(15) The weight of an object is 10 N on weighing. What will be its weight on moon?
Answer:
[98 N]

(16) A block of wood is kept on a table top. The mass of wooden block is 5 kg and its dimcnsions are 40 cm x 20 cm x 10cm. Find the pressure exerted by the wooden block on the table top ¡fit is made to lie on the table top with its sides of dimensions (a) 20 cm x 10 cm and (b) 40 cm x 20 cm.
Answer:
[(a) 2450 Nm^-2 (b) 612.5 Nm^-2]

(17) The relative density of silver is 10.8 g. The density of water is 1 kgm3. What will be the density
of silver in SI unit?
Answer:
[10.8 x 10³ kg m³]

Essay Type Questions

Question 1.
Find the deflnition of universal gravitational constant ‘G’. Write the unit of ‘G’ In SI system.
Answer:
According to Newton’s Universal Law of Gravitation,

F = \(\mathrm{G} \frac{\mathrm{M}_1 \mathrm{M}_2}{\mathrm{R}^2}\)
Or G = \(\frac{\mathrm{FR}^2}{\mathrm{M}_1 \mathrm{M}_2}\)
If M₂ = M₂ = 1 unit and R = 1 unit, then
G = \(\frac{F \times 1^2}{1 \times 1}=\frac{F \times 1}{1 \times 1}\) = F
∴ Thus, universal gravitational constant is a gravitational force which is placed between the objects of unit mass which are at unit distance from each other.

SI unit of G:
G = \(\frac{\mathrm{FR}^2}{\mathrm{M}_1 \mathrm{M}_2}\)
Because G is the ratio ofF and M1 M2/R2 . Therefore, its unit depends upon the units of force, mass and distance. If mass is taken in kilogram, distance in metres and time in seconds, then unit of force is newton (N). Therefore, unit of G will be Nm^-2 kg^-2. The value of G found by the experiments on golden balls is:
G = 0.000,000,000,066,734 Nm² kg²
= 6.673 x 10^-11 Nm² kg²

Question 2.
State the universal law of gravitation. Derive the formula for gravitational force between two bodies. Aand B of masses M and m, placed at a distanced.\(1 \frac{1}{2}+2 \frac{1}{2}=4\)
Answer:
Universal Law of Gravitation:
Every object in the universe attracts every other object with a force which is proportional to the product of their masses and inversely proportional to the square of the distance between them. The force is along the line joining the çentres of two objects.

Let two objects A and B of masses M and ‘m’ lies at a distance ‘d’ from each other as shown in figure. Let the force of attraction between two objects be F. According to the universal law of gravitation, the force between two objects is directly proportional to the product of their masses, that is,
F ∝ M x m …………(i)
And the force between two objects is inversely proportional to the square of the distance between them, that is,
F ∝ \(\frac{M \times m}{d^2}\) ………..(ii)
Combining eqs. (i) and (ii), we get
F ∝ \(\frac{M \times m}{d^2}\) or F = G \(\frac{M \times m}{d^2}\)
Where G is the constant of proportionality and is called universal gravitational constant.

Question 3.
Compare the weights of body if that are weigh on earth and moon.
Answer:
The value of acceleration due to gravity of each planet (g) depends upon its mass and radius. Due to this reason, weight of an object on moon is \(\frac {1}{6}\) th times than on the earth. Suppose the mass of object is ‘m’_e. If the mass of earth is Me and its radius is R_e, then weight of the object on earth (F_e).
F_e = \(\frac{\mathrm{GM}_{\mathrm{e} \mathrm{m}}}{\mathrm{R}_{\mathrm{e}}^2}\) ………..(i)
In same way, the mass of the moon is M_m and its radius is Rm then weight of the object on moon (F_m)
F_m = \(\frac{\mathrm{GM}_{\mathrm{e}} \mathrm{m}}{\mathrm{R}_{\mathrm{e}}^2}\) ………(ii)
Dividing eQuestion (i) by eQuestion (ii) \(\frac{\mathrm{F}_{\mathrm{e}}}{\mathrm{F}_{\mathrm{m}}}=\frac{\mathrm{GM}_{\mathrm{e}} \mathrm{m}}{\mathrm{R}_{\mathrm{e}}^2} \times \frac{\mathrm{R}_{\mathrm{m}}^2}{\mathrm{GM}_{\mathrm{m}} \times \mathrm{m}}=\frac{\mathrm{M}_{\mathrm{e}}}{\mathrm{M}_{\mathrm{m}}}\left(\frac{\mathrm{R}_{\mathrm{m}}}{\mathrm{R}_{\mathrm{e}}}\right)^2\)
∴ The mass of the earth is 100 times than that of moon, and radius is 4 times more
M_e = 100 M_m and
R_e = 4 R_m

By putting the value of M_e and R_e
\(\frac{\mathrm{F}_{\mathrm{e}}}{\mathrm{F}_{\mathrm{m}}}=\frac{\mathrm{M}_{\mathrm{e}}}{\mathrm{M}_{\mathrm{m}}}\left(\frac{\mathrm{R}_{\mathrm{m}}}{\mathrm{R}_{\mathrm{e}}}\right)^2=\frac{100 \mathrm{M}_{\mathrm{m}}}{\mathrm{M}_{\mathrm{m}}} \times\left(\frac{\mathrm{R}_{\mathrm{m}}}{4 \mathrm{R}_{\mathrm{m}}}\right)^2\)
\(\frac{\mathrm{F}_{\mathrm{e}}}{\mathrm{F}_{\mathrm{m}}}\) = 100 x \(\frac {1}{6}\)
= 6 approx.
F_e = 6 F_m
Thus, it is clear that the mass of the object on the moon will be m, but its weight on the earth is 6 times more in compare to moon.

Question 4.
Write the difference between:
(i) Gravitational force and force of gravity
(ii) Centre of mass and centre of gravity.
Answer:
(i) The difference between gravitational force and force of gravity is as follows:

Gravitational Force	Force of Gravity:
1. The gravitational force is the force that arises between any two objects in the universe.	1. The force exerted between the earth and the object is called force of gravity.
2. The gravitational force exerted between two objects is proportional to the product of their masses.	2. The force of gravity is proportional to the masses of body.
3. The gravitational force exerted between the two objects is inversely proportional to the square of the distance between their centres.	3. The force of gravity is proportional to the acceleration due to gravity (g).
Gravitational Force	Force of Gravity:

(ii) Centre of mass and centre of gravity.
Suppose a giant body is made of many particles. Then it is possible for us to define that point where the whole of the mass of the body is concentrated. This point is called ‘centre of mass’. On the surface of earth or nearby it, where force of gravity is constant, centre of mass is only that point where the force of gravity on whole body can be experienced. In this state, the centre of mass is called centre of gravity.

Thus ‘centre of gravity’ of a body is that point, where the force of gravity is acting on the whole body as shown in fig. The centre of gravity of objects having regular size and uniform density lies on their geometrical centre. This can be balanced on a needle at the geometrical centre. For example, the centre of gravity of a spherical ball, or rectangular piece of wood or circular disc of metal is at their centre.

Practical Work

Experiment 1.
Describe an activity to understand the motion of moon from earth. Procedure:
(i) Take a piece of thread. Tie a small stone at one end.
(it) Hold the other end of the thread and whirl it round as shown in fig.
(iii) The direction of the motion of stone will be circular motion.
(iv) Now release the thread.
(v) Again, note the direction of motion of the stone.
Before the thread is released, the stone moves in a circular path with a certain speed and changes direction at every point. The change in direction involves change in velocity or acceleration. The force that cause this acceleration and keeps the body moving along the circular path is acting towards the centre. This force is called the centripetal force.

Experiment 2.
Explain an activity to understand the meaning of free fall of objects.

Procedure:
(i) Take a stone.
(ii) Throw it upwards.
(iii) It reaches a certain height and then it starts falling down.
We know that the earth attracts objects towards it. This is due to force of gravity. Whenever objects fall towards the earth under this force alone, we say that the objects are in free fall.

Experiment 3.
Prove with experiment that the gravitational force between two objects of general masses is weak.

Procedure:
Take a magnet. Take it near the iron pin kept near the piece of stone. You will see that the iron pin is not attracted towards piece of stone but towards the magnet. It proves that the gravitational force between stone and pin is very weak. So the iron pin is not attracted towards stone. In fact, the gravitational force between piece of stone and iron pin is very weak as compared to magnetic force. So the iron pin attracted towards magnet but not towards piece of stone. It is concluded that the gravitational force between two objects of general masses is weak.

Experiment 4.
Explain with an experiment that why iron sinks into the water while cork floats ?

Procedure:
(i) Take a beaker filled with water.
(ii) Take an iron nail and a cork of equal mass.
(iii) Place them on the surface of water.
(iv) You will observe that the cork floats and the nail sinks.
This is due to the difference in their densities. The density of a substance is defined as the mass per unit volume. The density of cork is less than the density of water. This means that the up thrust of water on the cork is greater than the weight of the cork. So it floats.

Quick Review of the Chapter

1. What is the force of attraction called between the two particles of the universe ?
(A) force of gravity
(B) gravitational force
(C) centripetal force
(D) magnetic force
Answer:
(B) gravitational force

2. The force exerted by the earth on an object is called :
(A) force of gravity
(B) gravitational force
(C) centripetal force
(D) magnetic force
Answer:
(A) force of gravity

3. The acceleration which maintains the circular motion always directed towards the centre of circle, that is called :
(A) force of gravity
(B) gravitational force
(C) centripetal force
(D) buoyant force
Answer:
(C) centripetal force

4. Every object in the universe attracts every other object with a force which is proportional to the product of their masses and inversely proportional to the square of the distance between them. This law is called :
(A) universal law of gravitation
(B) law of gravity
(C) universal law of centripetal
(D) Archimedes’ principle
Answer:
(A) universal law of gravitation

5. The magnitude of the gravitational force on an object on the surface of earth is :
(A) \(\frac{\mathrm{GM}_{\mathrm{e}}}{\mathrm{R}^2}\)
(B) \(\frac{\mathrm{GM}}{\mathrm{R}^2}\)
(C) \(\mathrm{GM}_{\mathrm{e}} \mathrm{m}\mathrm{R}_{\mathrm{e}^2}\)
(D) \(\frac{\mathrm{M}_{\mathrm{e} m}}{\mathrm{GR}^2}\)
Answer:
(C) \(\mathrm{GM}_{\mathrm{e}} \mathrm{m}\mathrm{R}_{\mathrm{e}^2}\)

6. The value of gravitational constant is :
(A) different at each place on earth
(B) same at all planets and satellites
(C) vary from place to place
(D) all above statements are false
Answer:
(B) same at all planets and satellites

7. On which part of earth the value of acceleration due to gravity (g) is maximum?
(A) on poles
(B) on equator
(C) on centre
(D) on all of them
Answer:
(A) on poles

8. What is the weight of an object on moon in comparison of earth ?
(A) 6 times
(B) 3 times
(C) \(\frac {1}{6}\) times
(D) \(\frac {1}{3}\) times
Answer:
(C) \(\frac {1}{6}\) times

9. The value of acceleration due to gravity (g) is :
(A) same at every place on earth
(B) same at all planets and satellites
(C) vary from place to place
(D) all above statements are false
Answer:
(C) vary from place to place

10. If the weight of a person is 24 N on the earth, then what will be his weight on moon ?
(A) 6N
(B) 8N
(C) 4N
(D) 96 N
Answer:
(C) 4 N

11. The value of acceleration due to gravity (g) is least on which part of earth ?
(A) on poles
(B) on equator
(C) on mountains
(D) on all above
Answer:
(B) on equator

12. The formula of the attractive force (F) between two objects of masses ntj and m2 respectively kept at a distance of R is :
(A) \(\frac{\mathrm{Gm}_1}{\mathrm{~m}_2 \mathrm{R}^2}\)
(B) \(\frac{\mathrm{Gm}_2}{\mathrm{~m}_1 \mathrm{R}^2}\)
(C) \(\frac{\mathrm{R}^2}{\mathrm{Gm}_1 \mathrm{~m}_2}\)
(D) \(\frac{\mathrm{Gm}_1 \mathrm{~m}_2}{\mathrm{R}^2}\)
Answer:
(D) \(\frac{\mathrm{Gm}_1 \mathrm{~m}_2}{\mathrm{R}^2}\)

13. The value of acceleration due to gravity (g) on the surface of earth is :
(A) 9.8 ms^-2
(B) 4.9 ms^-2
(C) 19.6 ms^-2
(D) 29.4 ms^-2
Answer:
(A) 9.8 ms^-2

14. The value of acceleration due to gravity (g) is zero on :
(A) poles
(B) equator
(C) centre
(D) everywhere
Answer:
(C) centre

15. The value of acceleration due to gravity (g) at a distance of 12800 km from the centre of earth is:
(A) 1/4 th that of earth
(B) half of the acceleration due to
(C) 4 times that of earth
(D) gravity of earth double that of earth
Answer:
( A) 1/4 th that of earth

16. The distance of the moon from the earth is :
(A) 384000 m
(B) 384000 km
(C) 38400 km
(D) 38400 m
Answer:
(B) 384000 km

17. The quantity of matter present in the body is called :
(A) weight
(B) mass
(C) pressure
(D) thrust
Answer:
(B) mass

18. The weight of an object is zero at:
(A) poles
(B) equator
(C) mountains
(D) centre of earth
Answer:
(D) centre of earth

19. What is the relation among u, y, g and t?
(A) v = u + gt
(B) v + u = gt
(C) v + gt = u
(D) \(\frac {v}{g}\) = u + t
Answer:
(A) v = u + gt

20. The distance of sun from earth is approximately:
(A) 1.5 x 10¹¹ m
(B) 1.5 x 10¹¹ km
(C) 1.5 x 10¹¹ cm
(D) 1.5 x 10¹¹ mm
Answer:
(A) 1.5 x 10¹¹ m

21. By which symbol pascal is denoted?
(A) Pa
(B) Ps
(C) Pc
(D) P
Answer:
(A) Pa

22. On what angle a player throws ball with horizontal line so the ball falls at maximum distance?
(A) 900
(B) 0°
(C) 45°
(D) 600
Answer:
(C) 45°

23. The free fall means:
(A) the objects fàlling towards earth
(B) the objects going upward from the earth
(C) the objects moving parallel to earth
(D) none of these
Answer:
(A) the objects falling towards earth

24. SI unit of pressure is:
(A) Newton
(B) kilogram
(C) metre
(D) Pascal
Answer:
(D) Pascal

25. What will be the produced pressure 11300 n force is applied on the area of 20m2?
(A) 6000 Pa
(B) 3OPa
(C) 15 Pa
(D) 7.5 Pa
Answer:
(C) 15 Pa

26. It is difficult to hold a school bag having a strap made of a thin and strong string, because thrust affects:
(A) large area
(B) more area
(C) small area
(D) longer area
Answer:
(C) small area

27. When an object is immersed in a liquid, the liquid exerted an upward force, which is called:
(A) buoyant force
(B) gravitational force
(C) frictional force
(D) opposing force
Answer:
(A) buoyant force

Haryana State Board HBSE 9th Class Science Important Questions Chapter 9 Force and Laws of Motion Important Questions and Answers.

Haryana Board 9th Class Science Important Questions Chapter 9 Force and Laws of Motion

Very Short-Answer Type Questions

Question 1.
Define force.
Answer:
Force is that external factor that changes or tends to change the position of rest or speed and direction of moving object.

Question 2.
What is balanced force?
Answer:
When two or more forces acting on a body have zero resultant, then such forces are called balanced force.

Question 3.
What is unbalanced force ?
Answer:
When the resultant of two or more forces is not zero, such forces are called unbalanced force.

Question 4.
Which force works when a rubber ball is pressed between palms ?
Answer:
It is an example of a balanced force.

Question 5.
Which scientist has established the laws to control the motion of objects firstly?
Answer:
Sir Isaac Newton.

Question 6.
What is the angle of inclination?
Answer:
The angle made by an inclined plane with horizontal is called the angle of inclination.

Question 7.
Define frictional force.
Answer:
It is the opposing force that comes between the two surfaces in contact when a body moves or tends to move on another body.

Question 8.
Write the effect of frictional force.
Answer:
Frictional force reduces the motion of body.

Question 9.
Why the bicycle stops when we stop pedaling?
Answer:
The frictional force between the tyre of the bicycle and road reduces its motion and stops the bicycle.

Question 10.
Why powder is spread on the carom board in carom game?
Answer:
The powder is spread on the carom board to reduce the frictional force between carom board and coin.

Question 11.
What is the law of conservation of momentum?
Answer:
According to law of conservation of momentum, in absence of any external force, the total momentum of a system remains conserved.

Question 12.
Write Newton’s second law of motion?
Answer:
The rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of force. ‘

Question 13.
What is meant by momentum?
Answer:
The momentum of an object is the product of mass and velocity. It is denoted by p.
or p = mv

Question 14.
What is SI unit of momentum?
Answer:
Kilogram metre per second (kg ms^-1).

Question 15.
Momentum is a scalar quantity or vector.
Answer:
Momentum is a vector quantity, because it has both magnitude and direction.

Question 16.
In which direction, the momentum works ?
Answer:
Momentum works in the direction of velocity.

Question 17.
What is the relation among force, mass and acceleration ?
Answer:
Force = Mass x Acceleration (F = ma)

Question 18.
What is the SI unit of force ?
Answer:
The SI unit of force is Newton.

Question 19.
Define one Newton force.
Answer:
One Newton force is that force which produces an acceleration of 1 ms^-2 in a body of mass 1 kg.

Question 20.
What is negligible action ?
Answer:
When a body affects the other by applying force, then we say that there is negligible action between first and second body.

Question 21.
How many types of inertia is ?
Answer:
There is two types of inertia:
(i) Inertia of rest
(ii) Inertia of motion.

Question 22.
Write the concept of force on the basis of momentum.
F = \(\frac{p_2-p_l}{t_2-t_l}\)

Question 23.
How much force will be required to produce an acceleration of 2mS“2 in 6 kg object ?
Answer:
Force (F) = Mass (m) x Acceleration (a) = 6 x 2 = 12 N

Question 24.
A person pushes a box of 40 kg with a force of 80 N. What will be the acceleration of box ?
Answer:
Acceleration (a) = = 2 ms^-2

Question 25.
Write Newton’s third law of motion.
Answer:
According to Newton’s third law of motion, “The action and reaction are always equal and in opposite direction.”

Question 26.
What is inertia ?
Answer:
That property of objects which opposes the change in its motion or state of rest is called inertia.

Question 27.
Is the existence of a single force is possible ?
Answer:
No, the existence of a single force is not possible. The force is always in pairs.

Question 28.
Which force offers us the motion in a desired direction ?
Answer:
The force which offers us the motion in a desired direction is the reaction of the earth opposite to the force applied by our body.

Question 29.
Are the action and reaction imposed on an object ?
Answer:
No, action and reaction (force) are imposed on two different objects.

Question 30.
Write the name of two forces which arise without the contact of two objects.
Answer:
(i) magnetic force
(ii) force of gravity.

Question 31.
How the fruit from tree falls towards the earth ?
Answer:
Due to force of gravity.

Question 32.
Why is it difficult to climb on a smooth pole ?
Answer:
Due to less reaction.

Question 33.
Why oil is used in machines ?
Answer:
To reduce the friction.

Question 34.
Why is it difficult to walk on sand ?
Answer:
Due to more friction between feet and sand.

Question 35.
Compare the frictional force between the surfaces of solids and liquids.
Answer:
The frictional force between the surfaces of liquids is much less than the frictional force between the surfaces of solids.

Question 36.
A small piece of stone and a truck are moving with same motion. On which, the larger force will be imposed to stop both of them ?
Answer:
The larger force will be required to stop the truck, because it will have large momentum.

Question 37.
By which force, we can walk on road without slipping.
Answer:
Due to frictional force, we can walk on road without slipping.

Question 38.
Why it becomes difficult to walk on a green mossy road in rainy season ?
Answer:
The frictional force becomes less on mossy road so it becomes difficult to walk on such a road.

Question 39.
Which Newton’s law of motion helps us in the measurement of force ?
Answer:
Newton’s second law of motion helps us in the measurement of force.

Question 40.
According to which Newton’s Law of motion, jet aeroplanes fly ?
Answer:
They fly according to Newton’s third law of motion.

Question 41.
Why the player runs before jump ?
Answer:
To increase the momentum so that the jump can be high.

Question 42.
Force is a scalar quantity or Vector.
Answer:
Force is a vector quantity.

Question 43.
What is the total momentum of rifle and bullet after firing from rifle ?
Answer:
Zero.

Question 44.
How much acceleration will be produced if 1 newton (N) force is applied on an object of 1 kg mass ?
Answer:
1 ms^-2

Short-Answer Type Questions

Question 1.
What is meant by force ? What can be the effect on object by applying force on that ?
Answer:
Force is that external factor which changes or tends to change the position of rest or speed and direction of moving object.
Effects:
Following are the effects on body, when force is applied :
(i) Speed of object can be changed due to which the object moves fast or slow.
(ii) The direction of motion of object can be changed and can move body in rest.
(iii) Shape of the object can be changed.

Question 2.
Give five examples of force in daily life.
Answer:
Examples of force in daily life are as follows :
(i) When a force is applied on a rubber ball, it elongated. It is due to force.
(ii)When a spring is stretched, its length increases due to muscular force.
(iii) The steam gives its energy to steam engine due to that the steam engine moves forward.
(iv) A rolling ball can be stopped by muscular force.
(v) Petrol produces mechanical force by its energy, due to that bus, car etc. moves.

Question 3.
What is inclinded plane ? What are its uses ?
Answer:
A smooth plane which makes an angle with horizontal plane is called inclinded plane, e.g. knife, axe, screw, hilly roads, stairs etc. A man lifting a heavy weight with the help of inclinded plane made of wooden piece is shown in below fi.

Uses of inclinded plane:
The uses of inclinded plane are as follows:
(i) A heavy weight can be lifted by small force by using inclinded plane.
(ii) Heavy weight is loaded or unloaded in trucks by using it.
(iii) Screw also works on the principle of inclinded plane.

Question 4.
Distinguish between balanced and unbalanced forces.
Answer:
The difference between balanced and unbalanced forces are as follows :
Balanced Force Unbalanced Force
1. When balanced forces act together on a body, their resultant is zero.
2. The balanced force can’t move a body which is in rest position.
3. This force cannot change the speed and direction of moving body.
4. This force always changes the size of body.

1. When unbalanced forces act together on a body, their resultant is not zero.
2. The unbalanced force can move a body which is in rest position.
3. This force can change the speed and direction of a moving body.
4. This force does not always change the size of body.

Question 5.
What is meant by inertia ? Clarify by example.
Answer:
The property of bodies which opposes the change in motion of body or state of rest is called inertia.

Experiment:
Set a coin on a stiff playing card covering an empty glass tumbler. Give the card a sharp horizontal flick with a finger. You will see the card moves ahead but the coin will fall in glass. When the card is shoot fast, then due to property of inertia, the coin tries to remain in rest position. In this way, when the card moves, the coin falls in glass.

Question 6.
What are the types of inertia ? Explain with example.
Answer:
Inertia is of two types:
1. Intertia of rest: The property of body by which the body resists its rest position until an external force is not applied on it.
Example: A book on table does not move due to inertia of rest.

2. Inertia of motion: The property of body by which it resists its state of motion, until an external force is not applied on it.
Example: A passenger sitting in a bus or cart falls forward when the moving bus or cart stops suddenly. In such situation, the lower portion of body of passenger comes in rest as the bus or cart stops, but the upper portion tries to remain in motion, due to this passenger falls forward. –

Question 7.
What happens when a wet cloth is jerked ? Clarify your explanation.
Answer:
When we jerk the wet cloth, the cloth displaced from its position to inertia and they detached from cloth and escape in environment. Thus, the cloth dries fast.

Question 8.
In javelin throw, if a player crosses the fixed line, he fouls, but the playes usually fail to stop on this line, why ?
Answer:
When in javelin throw competition, a player runs and reaches the fixed line, his whole body comes in motion. When he tries to stop his feet on fixed line, the upper portion remains in motion due to inertia of motion and the player crosses the fixed line and fouls.

Question 9.
Why the rider falls backward when the horse starts running suddenly?
Answer:
The rider falls backward when the horse starts running suddenly because due to suddenly running the horse, it comes in motion but the rider tries to remain in rest due to inertia of rest and falls backward.

Question 10.
Why the rider falls forward when a running horse stops suddenly?
Answer:
The rider falls forward when a running horse stops suddenly because the horse and rider are in motion when it is running and when horse
stops suddenly it comes in rest but the rider tries to remain in motion due to inertia of motion and falls forward.

Question 11.
Why are the tyres of vehicles made rough and treaded ?
Answer:
The movement of vehicles is due to the frictional force between road and tyres. If their tyres are smooth then the friction will be less betw een road and tyre, so that it will be difficult to control the vehicle. In order to control vehicles, the tyres are made rough and treaded so that the friction between tyre and road increases and grip of tyres with road will be firm.

Question 12.
Define and explain Newton’s first law of motion.
Answer:
Newton’s first law of motion:
An object continuous to be a state of rest or of uniform motion along a straight line unless acted upon by an unbalanced force. This law is also known as “Galileo’s Law of Inertia.” e.g. a ball rolling on floor can move far due to less friction. If the friction reduces to zero by any mean, the ball will move with initial velocity for a certain time.

Question 13.
Prove that Newton’s first law of motion can be called the law of inertia.
Answer:
According to Newton’s first law of motion, an object continuous to be a state of rest or of uniform motion along a straight line unless acted upon by an unbalanced force. In other word, all objects oppose the change in their state of motion. This tendency of the objects to oppose the change in their state of motion is called inertia. Thus, Newton’s first law of motion is also called the law of inertia.

Question 14.
Prove that the mass of a body is the measure of its inertia.
Answer:
The quantity of matter in a body is its mass. In this way, the mass is the measure of inertia of body. A body having large mass has large inertia.

Explanation:
If we kick a football it moves so far. but if we kick a stone, it will not move and our foot gets wound, because in comparison of football, stone has larger capacity to oppose the change in motion due to its larger mass. The mass of a body is the measure of its inertia.Thus, the inertia of a stone is more.

Question 15.
Define and explain Newton’s second law of motion with the help of this law, obtain equation of force.
Answer:
Newton’s second law of motion : The force applied on a body is proportional to the product of its mass and acceleration. If we kick a ball, it will move quickly because its acceleration becomes more. In this way, a cricketer stops a moving ball slowly, so that the change in motion of ball takes much time. He moves his hands in the direction of ball and the acceleration of ball becomes less in comparison of initial and less force is required to stop the ball. Let us consider a body has mass m and a force F produces an acceleration a in it. According to Newton’s second law of motion,
F ∝ m x a
or F = K ma ………..(i)
here, K , is a constant, whose value depends upon the units of mass, force and acceleration.
Let m = 1 kg, a = 1 m s^-2 and f = 1 N
then, putting the value of F, m and a in eQuestion (i)
1 = K x 1 x 1
or K = 1
F = 1 x ma
Force = Mass x Acceleration

Question 16.
Define and explain Newton’s third law of motion.
Answer:
Newton’s third law of motion:
To every action, there is an equal and opposite reaction and they act on two different bodies. Action and reaction are equal and in opposite direction.

For example:
(i) A ball presses the earth with a force, the earth pushes the ball upwards with same force.
(ii) When a person swims, he pushes the water backward, he moves forward, by this reaction.

Question 17.
Explain why does cricket player pulls his hands backward while catching a fast moving cricket ball ?
Answer:
The momentum of moving ball is more. When player catches the ball, he pulls his hands backward so that momentum of ball takes some time to become zero. In this way, momentum of ball, rate of change and the force applied on hand will become less and there is no hurt on hands.

Question 18.
Why larger force is required to stop a ship than car moving on road ?
Answer:
The frictional force between the tyres of car and road is more. Therefore the car stops quickly by applying lesser force. The frictional force between the surfaces of liquids is much less than the frictional force between the surfaces of solids. Due to this reason, the ship experiences less friction in water. Thus, larger force is required to stop a ship than car.

Question 19.
When there is negligible reaction between two bodies how the direction changes when two moving objects strike? Clarify with figure.
Answer:
When there is negligible reaction between two bodies, one body affects the other by force. The collision between two marbles is an example of negligible reaction. In figure two marbles are shown moving towards each-other. The direction of their motion is shown by arrow. It is clear from figure that the direction of marble changes after collision. Two forces act in this action. One is that which has accelerated one marble and second is that which has accelerated the other marble.

Question 20.
What is meant by action and reaction ? What is the relation between them ? In which law of motion, these are described ?
Answer:
If a body applies some force on other, then it is the active force on other body. In response, the force which second body applied on first is the reactive force on first body. The relation between action and reaction : The force of action and reaction are equal and in opposite directions. An important fact is that the force of action and reaction always act on different bodies. These are described in third law of motion.

Question 21.
Give some examples of Newton’s third law of motion in daily life.
Answer:
Following are the examples of Newton’s third law of motion :
(i) The bullet moves forward when trigger is pressed and due to reaction force, the gun recoils backward.
(ii) The person pushes the water backward while swimming and moves forward due to tne reaction or
water.
(iii) When a person jumps from boat at river-shore, the boat displaced far from shore due to reaction of water on that.
(iv) We press the earth backward while walking and
due to force of reaction the earth pushes our feet forward and we move. .
(v) The ores push the water backward and due to reaction, the boat move forward.
(vi) When a player jumps up, he pushes the surface of earth downward, so that he gets reaction.

Question 22.
Why the boat moves in opposite direction when a person jumps to shore from the boat ? Explain.
Answer:
A person applies force in upward to get the necessary motion at the time of jumping from boat. His reaction is on boat, which according to Newton’s third law of motion is in opposite direction. As a result of this, the boat move far on opposite direction.

Question 23.
Explain in brief, the relation between Newton’s first and second law of motion.
Answer:
The Newton’s first law of motion is the part of second law. It can be clarify on the basis of following fact:
According to second law of motion,
F = m a
if F = 0, then
m a = 0 m = 0,
a = 0
But mass, m cannot be zero, because it is a constant quantity. So, if acceleration a is zero, the change in velocity will also be zero. Therefore, there is no change in the position of body. If it is in rest, it will remain in rest, and if it is in motion, it will remain in motion unless external force is not applied. This is the statement of Newton’s first law of motion. Thus Netwon’s first law of motion is the part of second law.

Question 24.
What is the reason that a fast moving bullet makes a round hole in glass but on throwing the stone, the glass damages ?
Answer:
The size of bullet is small and that of stone is big so that the glass does not move when bullet is striked, only that part move where the bullet is striked and makes a hole, but there is no hole when stone is striked because whole glass moves and damaged.

Numerical Questions

Question 1.
Speed-time graph of a moving coin on table is shown in fig. . The weight of coin is 10 g.
How much force the table exerts to stop the coin?
Solution:
Here,
Initial velocity (u) = 24 ms^-1
Final velocity (v) = 0 ms^-1
Time (r) = 8 sec
Mass (m) = 10g = \(\frac {10}{1000}\) kg

We know that,
Acceleration (a) = \(\frac{v-u}{t}=\frac{0-24}{8}\) = \(\frac {-24}{8}\) = -3 ms^-2
∴ Force(F) = m.a
\(\left(\frac{10}{1000} \times-3\right)\) N
= – 0.03 N
(- ve sign shows that force decreases the motion.)

Question 2.
A cricket ball of mass 70g is moving with a velocity of 0.5 ms^-1. A cricket player stops it in 0.5 s. Calculate the force applied by the player to stop
the ball.
Solution:
Mass of the ball (m) 70g =\(\frac {70}{1000}\)= 0.07 kg
Initial velocity of ball (u) = 0.5 ms^-1
Final velocity of ball (v) = 0
The time taken to stop the ball, (t) = 0.5s
We know that, v = u + at
a = \(\frac{v-u}{t}=\frac{0-0.5}{0.5}=\frac{-0.5}{0.5}\) = -1 ms^-2
Thus, the force applied by the player to stop the ball
(F) = ma
= 0.07 x -1N = -0.07 N
(-ve sign shows that force is working against momentum.)

Question 3.
How much acceleration will be produced in the object ¡fa force of 200 N is applied on an object of 5 kg mass?
Solution: Here,
Mass(m) = 5kg
Force (F) = 200N
Acceleration (a) = ?
We know that, F = ma
a = \(\frac{F}{m}=\frac{200}{5}\) = 40 ms^-2

Question 4.
A constant force is working on an object of 5 kg mass for 2 seconds. It increases the velocity of object from 3ms1 to 7ms^-1. Calculate the value of applied force. Now, what will be the final velocity if the force works for 5 seconds on object?
Solution:
Here,
Mass of object (m) = 5 kg
Initial velocity of object (u) = 3 ms^-1
Final velocity of object (v) = 7 ms^-1
Time (t) = 2s
Acceleration (a) = ?
We know that.
a = \(\frac{v-u}{t}=\frac{7-3}{2}\)ms^-2 = \(\frac {4}{2}\) = 2 ms^-2
The force applied on object (F) = ma
= 5 x 2 = 10 N

In second stage,
Initial velocity of object (u) = 3 ms^-1
Final velocity of object (v) = ?
Time (t) = 5s
Acceleration (a) = 2 ms^-2
We know that,
v = u + a = 3 + 2 x 5 = 13 ms^-1

Question 5.
How much force is required to stop a car of mass 1000 kg and a loaded truck of mass 10,000 kg moving both with a velocity of 5ms in 2 seconds?
Solution:
Here.
Initial velocity of both (u) = 5ms
Final velocity of both (v) = O
time (t) = 2 s
Acceleration (a) = ?
We know that, v = u + at
a = \(\frac{v-u}{t}=\frac{0-5}{2}=\frac{-5}{2}\) = ms^-1

Mass of the car (m₁) = 1000 kg
Mass of the truck (m₂) = 10,000 kg
The necessary force to stop the car (F₁) = m₁ a
= 1000 x \(\frac {-5}{2}\) N
= – 2500 N
Thus, necessary force to stop the car = – 2500 N
(-ve sign shows that force is working against momentum.)
In same way, the necessary force to stop the truck (F₂) = m₂ a
= 10000 x \(\frac {-5}{2}\)N
= – 25000 N
Therefore, the necessary force required to stop the truck is more than that of car.

Question 6.
Which will require more force – to accelerate a body of mass 2 kg with a rate of 5 ms^-2 or to accelerate a both of mass 4kg with a rate of 2 m^-2?
Solution:
Here,
m₁ = 2kg
a₁ = 5 ms^-2
Force (F₁) = m₁a₁ = 2 x 5 = 10 N
m₂ = 4 kg
a₂ = 2 ms^-2
Force(F₂) = m₂a₂ = 4 x 2 = 8N
In this way F₁> F₂
∴ Large force will required to accelerate the object of 2 kg mass with a velocity of 5 ms^-2

Question 7.
A bullet of mass 20 g is horizontally fired with a velocity of 150 ms from a pistol of mass 2 kg. What is the recoil velocity of the pistol?
Solution:
Mass of bullet, m₁ = 20 g ( = 0.02 kg)
Mass of pistol. m₂ = 2 kg
The initial velocity of bullet (u₁) and pistol (u₂) is zero, respeciively.
That is u₁ = u₂ = 0
Final velocity of bullet, v₁ = + 150 ms^-1
The direction of bullet is taken + ve according to left to right system. Suppose, recoil velocity of pistol is v.
Total momentum of bullet and pistol before firing = (2 + 0.02) kg x o ms^-1
= 0 kg ms^-1
Total momentum after firing = 0.02 kg x (+ 150 ms^-1) + 2 kg x v ms^-1
= (3 + 2v)kg ms^-1
According to the law of conservation of momentum,
Total momentum after firing = Total momentum before firing
3 + 2v = 0
2v = -3
v = \(\frac {-3}{2}\)
v = -1.5 ms^-1
(-ve sign shows that the pistol recoils opposite to the direction of bullet i.e. right lo left.)

Question 8.
A coin is moving with a velocity of 24 cm s rolls with an acceleration of 3 cm² and stops in 8 s. Find the distance covered by the coin.
Solution:
Here,
Initial velocity (u) = 24 cm s
Final velocity (v) = 0
Acceleration (a) = – 3 cm s²
Time (t) = 8s
Distance (s) = ?
We know that, Distance (s) = ut + \(\frac {1}{2}\) at
= 24 x 8 + \(\frac {1}{2}\) x (-3) x (8)²
= 192 – 96
= 96 cm

Question 9.
In which the more force will require-to produce an acceleration of 5 ms in mass 10 g or to produce an acceleration of 2 ms2 in mass 20 g?
Solution:
In first stage, Mass (m) = 10 g = \(\frac {10}{1000}\) kg
Acceleration (a) = 5 ms^-2
The necessary force (F) = m x a
= \(\frac {10}{1000}\) x 5
= 0.05 N
In second stage, Mass (m) = 20 g = \(\frac {20}{1000}\) kg
Acceleration (a) = 2 ms^-2
The necessary force (F) = m x a = \(\frac {20}{1000}\) x 2 = 0.04N
Thus, larger force will be required to produce an acceleration of 5 ms2 in an object of mass 10 g. Answer:

Question 10.
A bullet of mass 20 g moving with a velocity of 16 ms^-1 enters ¡n a sand bag and comes in rest after 0.05 s. Find,
(a) depth of penetration ¡n sand
(b) the average resistive force applied by sand.
Solution:
Here,
(a) Initial velocity (u) = 16 ms^-1
Final velocity (v) = 0
Time (t) = 0.05 s
Distance (s) = ?
Average resistive force (F) = ?

We know that,
Acceleration (a) = \(\frac{v-u}{t}=\frac{0-16}{0.05}\) = 0.05
= \(\frac{v-u}{t}=\frac{0-16}{0.05}\)
= \(\frac{-16 \times 100}{5}\) = – 320 ms^-2
s = ut + \(\frac {1}{2}\) at²
= 16 x 0.05 + \(\frac {1}{2}\) x (-320) x (0.05)²
or s = 0.8 – 0.4 = 0.4m
(b) Mass (m) = 20 g = \(\frac {20}{1000}\) kg
Average resistive force (F) = m x a = \(\frac {20}{1000}\) x -320 = -6.4 N

Question 11.
How much will be the change in momentum of an object of mass 5kg, If Its speed:
(i) reduces from 20 ms^-1 to 0.20 ms^-1
(ii) Increases from 30 ms¹ to 40 ms^-1.
Solution:
Here,
Mass of the body (m) = 5kg
Initial velocity (u) = 20 ms¹
Final velocity (v) = 0.20 ms¹
Initial momentum (p₁) = m x u = 5 x 20 = 100 kg ms^-1
Final momentum (P₂) = m x v = 5 x 0.20 = 1.00 kg ms^-1
Thus, decrease in momentum = p₁ – p₂ = 100 – 1 = 99 kg ms^-1
Initial velocity (u) = 30 ms¹
Final velocity (v) = 40 ms¹
initial momentum (p₁) = m x v = 5 x 30 = 150 kg ms^-1
Final momentum (p₂) = m x v = 5 x 40 = 200 kg ms^-1
Thus, increase in momentum = 200 – 150 = 50 kg ms^-1

Question 12.
A driver accelerates a car In first stage with 1.8 ms^-2 and in second stage with 1.2 ms^-2 acceleration. Find the ratio of forces applied by engine in both stages.
Solution:
Let,
The mass of car = m kg
Acceleration in first stage = (a₁) = 1.8 ms^-2
∴Force in first stage (F₁) = m x a₁ = m x 1.8m = 1.8 m N
Acceleration in second stage (a₂) = 1.2 ms^-2
∴Force in first stage (F₂) = m x a₂ = m x 1.2 = 1.2m N
\(\frac{F_1}{F_2}=\frac{1.8 \mathrm{~m}}{1.2 \mathrm{~m}}=\frac{18}{12}=\frac{3}{2}\)
F₁:F₂ = 3:2

Question 13.
On applying a force for 1.2 s on an object, its speed increases from 1.8 ms^-1 to 4.2 ms^-1. The same force is applied for 2 s again. How much change in speed will be in 2s?
Solution:
Initial velocity in first stage (u) = 1.8 ms^-1
Final velocity (v) = 4.2 ms^-1
Time (t) = 1.2 s
According to formula, v = u + at
or u + at = v
1.8 + a x 1.2 = 4.2
or 1.2a = 4.2 – 1.8
or 1.2a = 2.4
or a = \(\frac {2.4}{1.2}\) = 2 ms^-1
∴ Acceleration = 2 ms^-2
initial velocity in second stage (u) = 4.2 ms
Time (t) = 2s
Acceleration (a) = 2 ms2
Final velocity (v) = u + at = 4.2 + 2 x 2 = v = 4.2 + 4 = v = 8.2 ms^-1
Thus, change in speed in 2s = 8.2 – 4.2 = 4 ms^-1

Do Yourself

(1) How much force will require to produce an acceleration of 2ms2 in an object of mass 12 kg? What
will be the acceleration, if force is doubled?
Answer:
24N, 4 ms^-2

(2)Aperson pushes a box of mass 50kg by a force of 80 N. What will be the acceleration of box ? What will be the acceleration of box if its mass is reduced to half?
Answer:
1.6 ms^-2, 3.2 ms^-2

(3) A motorcycle is moving with a velocity of 90 kmh1 and on applying brakes, stops in 5s. Calculate the force applied by brake on motorcycle, if its mass including driver is 200 kg.
Answer:
1000 N

(4) A rifle of mass 3 kg fires a bullet of mass 0.03 kg. The bullet leaves the barrel of the rifle at a velocity of 100 ms. ¡f the bullet takes 0.003 second to move through the barrel, calculate the force experienced by the rifle due to its recoil.
Answer:
1000 N

(5) Calculate that force which offers a velocity of 30 ms in lOs to a car, if the mass of car is 1500 kg.
Answer:
4500 N

(6) A car starts from rest and moves for 2 minutes with an uniform acceleration of 0.1 ms2. Calculate the distance covered by the car.
Answer:
720 m

(7) Calculate that force which will produce an acceleration of 0.40 ms^-2 in a toy car of mass 0.25 kg.
Answer:
0.1N

(8) An object is dropped froma height of 20 metres. 1f g = 10 ms^-2 then, calculate the velocity when it strikes to earth. Find the time taken to fall from that height.
Answer:
20 ms^-1, 2s

(9) The velocity-time graph of a ball of mass 20 g moving in straight line on a long table is giyen in figure. How much force will be table offer to ball to take it in rest?

Answer:
0.0004 N

(10) A bullet of mass 10 g leaves the barrel with a velocity of 300 ms1 in 0.0035 s. How much force was exerted by the rifle on bullet?
Answer:
857.14 NJ

(11) A car is moving with a speed of 108 kmh1 and takes 4s to stop after applying brakes. Calculate the force on car after applying brakes. Total mass of car including passengers, is 1000 kg.
Answer:
750 N

(12) A force of SN produces an acceleration of 10 ms^-2 in mass m1 and 20 ms^-2 in mass ms^-2. What will be the acceleration produced by this force, if both the masses are combined?
Answer:
6.67 ms^-2

(13)A resultant force of 15 N is applied on an object kept on a frictionless horizontal plane produces an acceleration of 5 ms^-2. Find the mass of object.
Answer:
3kg

(14) On applying a force of 5 N on mass in1, an acceleration of 8 ms2 is produced and by applying same force on mass ms^-2, produces an acceleration of 24 ms^-2 . How much acceleration will be produced by in combined mass by this force. 1f both masses becomes one by tieing?
Answer:
6 ms^-2

(15) Two hockey players of opposite teams, while trying to hit a hockey ball in the ground collide and immediately get entangled. One has a mass of 60 kg and is moving with a velocity of 5 ms^-2 while the other has a mass of 55 kg and is moving faster with a velocity of 6 ms towards the first player. In which direction and with what velocity will they move after they get entangled ? Assume the frictional force between the feet of the two players and the ground is negligible.
Answer:
Right to left and with velocity of 0.26 ms

Essay Type Questions

Question 1.
How Galileo proved that the object will move with a ceaseless speed if a balanced force is not applied on that object?
Answer:
On the basis of experiments written ahead, Galileo first of all told that the object will move with a ceaseless speed if a balanced force is not applied on that object. Galileo studied the motion of objects on a double inclined plane. He observed that velocity of a body increases when it rolls down the inclined plane and decreases when it climbs upon as shown in fig.

Thus, he concluded that if the body moves on smooth plane then its speed neither increases nor decreases but its speed will remain ceaseless.
Now, he imagine that if a ball is allowed to go down by touching a hollow semi-spherical surface, it will reach the same height to which it was dropped. He concluded on the basis of motion of bob pendulum because the bob of pendulum attains that height from where it started moving. Semi-spherical surface works the same which thread does in pendulum.

After that he told that the shape of pot is taken as showm in fig., then the ball or object reaches the same height in this situation also. Yet, it has to cover large distance to do so.

Now, if the slope on the other side of pot is decreased, the ball covers the more distance to reach that height. In this way he concluded that if the slope is decreasing to one side of pot, the ball will cover the large distance. If there is no slope the surface becomes plane the ball will cover infinite distance and move with constant velocity.

Question 2.
What is the momentum of body ? Establish a relation between the momentum and force of a moving body.
Answer:
Momentum: The momentum of body is the product of its mass (m) and velocity (v). It is denoted by ‘p’
Momentum = Mass x Velocity
or p = mv
We know that a body accelerates if some force is applied to it. According to Newton’s second law of motion, the acceleration produced in a body depends upon the force applied on that. If by applying a force, ‘F’ on a body of mass m, produces an acceleration of ‘a’ then according to second law of motion
F = ma
a = \(\frac {F}{m}\) ………….(1)
Suppose, Initial velocity of body = v₁ms^-1
After time (t) the final velocity = v₂ ms^-1
Then a = \(\frac{v_2-v_1}{t}\)
From eqs. (i) and (ii) is
\(\frac{F}{m}=\frac{v_2-v_1}{t}\)
F = \(\frac{m\left(v_2-v_1\right)}{t}\)
F = \(\frac{m v_2-m v_1}{t}\)
But mv₁ = p₁ (Initial momentum)
and mv₂ = P₂ (Final momentum)
F = \(\frac{p_2-p_1}{t}\)
F = rate of chance of momentum.
Thus, the force applied on a body is equal to the change in momentum in unit time.

Question 3.
What do you understand by conservation of momentum ? Prove the law of conservation of momentum in mathematical way.
Answer:
Conservation Law of Momentum : According to this law, the total momentum of a group of objects remains constant until it is not act upon by external force.
Activity: To prove this law, suppose two objects A and B of mass m1 and m2 are moving with velocities u₁ and u₂ respectively. Let both react with each other till time t. After action, their velocities become v₁ arid v₂as
shown in fig.
if any external force does not act, then the rate of change in momentum of object A is m₁ \(\frac{\left(v_1-u_1\right)}{t}\) In the same way the rate of change in momentum of object B is m₂ \(\frac{\left(v_2-u_2\right)}{t}\) If a force F₁ is exerted on A by B and F₂ on B by A, then according to Newton’s second law of motion,

F₁ = m₁\(\frac{\left(v_1-u_1\right)}{t}\) ………….(1)
and F₂ = m₂\(\frac{\left(v_2-u_2\right)}{t}\) ………….(2)
According to Newton’s third law of motion, F₁ and F₂ act equally and ¡n opposite direction.
F₁ = -F₂ ………….(3)
From eqs. (1), (2) and (3), is
m₁ = \(\frac{\left(v_1-u_1\right)}{t}\) = m₂
or m₁(v₁ – u₁) = m₂ (v₂ – u₂)
or m₁v₁ – m₂u₁ = m₂v₂ + m₂u₂
or m₁v₁ + m₂v₂ = m₁u₁ + m₂u₂
or m₁ u₁ + m₂u₂ = m₁v₁ + m₂v₂ ………(4)

Thus, total momentum before collision m₁u₁ + m₂ u₂ is equal to total momentum after collision m₂v₂ . This is the law of conservation of momentum.

Question 4.
What is meant by friction ? Prove that it is a boon as well as curse.
Answer:
Friction: The opposing force that comes into play when a body moves on another surface or through a fluid (liquid or gas) is called friction.
Friction as a boon: The friction is a necessary evil because nothing is possible without it, that is:
(i) We cannot move if there is no friction between road and feet.
(ii) The vehicles cannot move if there is no friction between road and tyres.
(iii) The nail can be insisted in wall only due to friction.
(iv) Only due to friction, the match stick burns.
(v) It is possible to write on blackboard due to friction between chalk and blackboard.
(vi) Due to friction, we can write on copy.
(vii) The vehicles can be stopped only by friction.
(viii) The belts related to electric motors can move on wheels due to friction.

Friction as a curse: Besides a necessary evil, friction is harmful to us as:
(i) Due to friction the parts of machine get bear and tear.
(ii) Due to friction, the efficiency of machines is not 100%.
(iii) More energy is spent due to friction.
(iv) Due to friction, our shoes tear.
(v) Due to friction, the tyres of vehicles reduces.

Question 5.
Write the methods of reducing friction. Explain any one out of them.
Answer:
Methods of Reducing Friction : Friction can he reduced by following methods:
(i) The frictional force can be reduced by planing the depresions on the surface of body
(ii) Oil or lubricant educes the friction between two surfaces. Due to this the oil is put in the part machines and the friction can be reduced.
(iii) The mixture of water and soap can minimise the friction between two surfaces.
(iv) The friction can be minimize by using ball-bearings.
(v) When we sprinkle powder on a carom board, the powder tills up the depressions and the coin
(vi) In order to reduce friction, special shape is given to vehicles.
(vii) By polishing two surfaces and by putting coaltar on roads, the friction can be reduced.

To reduce the friction by using ball-bearIng : Ball-bearings are used in machines to reduce friction. Small balls are there in ball-bearings which are kept between the sliding surfaces of machines. You will have seen them in the wheels of cycle. These reduces the friction which save energy and work.

Practical Work ‘ .

Activity I.
Two activities to show the effect of force which proves that the force can change the size of body.

Procedure:
(i) Take a spring and pull it towards outside by holding its two ends. You, will see the size of spring increase, which shows the force applied on spring by us. It proves that the force can change the size of body.
(ii) Take a spherical rubber ball and press it between your palms. You will see that on pressing, the size of ball becomes some long. It proves that the force can change the size of body.

Activity 2.
Perform on activity to show that a body starts moving only when the force applied by us is more than frictional force.

Procedure:
Take a box and tell to children to push it. You will see that the box does not move if they apply less force, because the frictional force between the lower surface of box and rough surface of floor balances the force applied to push and due to this the box does not move. The children push the box with large force, but box does not move. This is because of that the friction force is still balances the pushing force. If the children push the box with much more force, then pushing force will become more than frictional force. Here, the unbalanced force is working and the box is moving. It proves that if the force applied by us is more than frictional force, the body moves.

Activity 3.
Perform an activity to show the effect of action and reaction. .

Procedure:
(i) Take a big rubber balloon and inflate it fully.
(ii) Tie its neck using a thread. Also using adhesive tape, fix a straw on the surface of this balloon.
(iii) Pass a thread through the straw and hold one end of the thread in your hand or fix it on the wall.
(iv) Now remove the thread tied on the neck of balloon.
(v) Now the air escape from the mouth of the balloon and the straw and balloon will move in opposite direction which shows reaction.

Procedure 2:
(i) Take a test tube of good quality glass material and put a small amount of water in it.
(ii) Place a stop cork at the mouth of it. Now suspend the test tube horizontally by two strings.
(iii) Heat the test tube with a burner until water vaporises and the cork blows out.
(iv) We observe that the test tube recoils in the direction

Quick Review of the Chapter

1. When a force is applied on a body, its :
(A) motion can change
(B) size can change
(C) direction of motion can change
(D) all of the above
Answer:
(D) all of the above

2. If the resultant of all forces acting on a body is zero, then all forces acting on body is called :
(A) balanced force
(B) unbalanced force
(C) frictional force
(D) none of these
Answer:
(A) balanced force

3. Unit of force is:
(A) joule
(B) metre per second square
(C) Newton
(D) metre per second
Answer:
(C) Newton

4. If the resultant of all forces acting on a particle is not zero, then forces are called:
(A) balanced force
(B) unbalanced force
(C) frictional force
(D) none of these
Answer:
(B) unbalanced force

5 Which scientist has established the laws of controlling the motion of objects firstly ?
(A) Sir Isaac Newton
(B) C.V. Raman
(C) Rutherford
(D) Neils Bohr
Answer:
(A) Sir Isaac Newton

6. Newton’s laws of motion are:
(A) 2 ‘
(B) 3
(C) 4
(D) 5
Answer:
(B) 3

7. Newton first law of motions is called:
(A) Law of friction
(B) Law of conservation of momentum
(C) Law of inertia
(D) Law of gravity
Answer:
(C) Law of inertia

8. The rate of change of momentum of a body is proportional to the force applied and in the direction in which force is applied. This is Newton’s:
(A) first law
(B) second law
(C) third law
(D) fourth law
Answer:
(B) second law

9. The product of mass and velocity of an object is called:
(A) momentum
(B) inertia
(C) friction
(D) force
Answer:
(A) momentum

10. SI unit of momentum is:
(A) kg^-2
(B) kg ms^-1
(C) kg m
(D) kg mh^-1
Answer:
(B) kg ms

11. The relation among F, m and a is:
(A) F = \(\frac {m}{a}\)
(B) Fa = m
(C) F = ma
(D) none of these
Answer:
(C) F = ma

12. The force required to produce an acceleration of 1 mc2 in a body of mass 1 kg is:
(A) 1 Newton
(B) 2 Newton
(C) 3 Newton
(D) 4 Newton
Answer:
(A) I Newton

13. The force which acts without the contact of two objects is:
(A) magnetic force
(B) inertia
(C) friction
(D) all of the above
Answer:
(A) magnetic force

14. According to which force, the apple faits on earth from tree?
(A) force of gravity
(B) inertia
(C) force of magnet
(D) frictional force
Answer:
(A) force of gravity

15. It is difficult to walk on sand because the friction between feet and sand is:
(A) less
(B) more
(C) normal
(D) not there
Answer:
(B) more

16. A piece of stone and a truck is moving with same speed. In order to stop both, which one will require more force to stop?
(A) truck
(B) stone
(C) none on them
(D) both require equal.
Answer:
(A) truck ‘

17. Which of the following force move the object?
(A) Gravitational force
(B) Unbalanced force
(C) Balanced force
(D) Frictional force
Answer:
(B) Unbalanced force

18. Why the lubricant is used in machines?
(A) To increase friction
(B) To decrease friction
(C) To zero friction
(D) To clarity
Answer:
(B) To decrease friction

19. The dust detached from carpet when beaten with stick because of:
(A) inertia of rest
(B) motion of carpet
(C) motion of stick
(D) force
Answer:
(A) inertia of rest

20. If an external force ¡s working on a body, It accelerates in the dxrection of force. The acceleration produced is proportional to:
(A) applied force
(B) velocity
(C) mass
(D) inertia
Answer:
(A) applied force

21. If the mass of two objects A and B is 6 kg and 34 kg respectively, then:
(A) the inertia of object A is more than B
(B) the inertia of B is more than A
(C) inertia of A and B are same
(D) inertia of A and B are zero
Answer:
(B) the inertia of B is more than A

22. According to Newton’s third law of motion, the force related to action and reaction should apply on:
(A) one body
(B) same bodies
(C) always different bodies
(D) is not necessary to have equal result but their direction should be same
Answer:
(C) always different bodies

23. The explanation of falling forward when get down from bus can be done by:
(A) Newton ‘s first law of motion
(B) Newton ‘s second law of motion
(C) Newton’s third law of motion
(D) all of the above
Answer:
(A) Newton’s first law of motion

24. Launching of rocket ¡s based on the principle of:
(A) Newton’s first law of motion
(B) Newton’s second law of motion
(C) Newton’s third law of motion
(D) all of the above
Answer:
(C) Newton’s third law of motion

25. If the mass of an object m, velocity y, acceleration a, then the momentum (p) will be:
(A) p = mv
(B) p = \(\frac {m}{a}\)
(C) p = ma
(D) p = \(\frac {m}{a}\)
Answer:
(A) p = mv

26. Which one of the following has mo inertia?
(A) a rubber ball
(B) a piece of stone
(C) a cycle
(D) a train
Answer:
(D) a train

27. The branch of a tree sheds its leaves when it is shedding fastly:
(A) due to mass
(B) due to inertia
(C) due to weight
(D) due to acceleration
Answer:
(B) due to inertia

28. If an object of mass 30 kg has the momentum of 120 kg ms’, then its velocity will be:
(A) 4 ms^-1
(B) 8 ms^-1
(C) 2 ms^-1
(D) 1 ms^-1
Answer:
(A) 4 ms^-1

29. When a running bus stops suddenly, you falls forward and when starts running suddenly from rest you falls backward, It Is
(A) due to mass
(B) due to weight
(C) due to motion
(D) due to inertia
Answer:
(D) due to inertia

30. The mass of a cart is 1500 kg. If the cart is to bring in rest with negative acceleration (retardation) of 1.7 ms^-2, then the force between the cart and road will be
(A) 882.35 N
(B) 2550 N
(C) 1500N
(D) 2550 kgm
Answer:
(B) 2550 N

31. A bullet of mass 10 g moving in a straight line with a velocity of 150 ms^-1 strikes with a wooden piece and stops after 0.03 s. How far the bullet will penetrate the wood?
(A) 2.25 km
(B) 2.25 m
(C) 22.5m
(D) 15m
Answer:
(B) 2.25 m

32. A body of mass 1 kg moving in a straight line with a velocity of 10 ms^-1 strikes with a wooden piece of mass 5 kg which is in rest. After that both move in straight line together. The total momentum before collision will be
(A) 10 kg ms^-2
(B) 2 kg ms^-1
(C) 50kgms^-1
(D) 10kg ms^-1
Answer:
(D) 10kg ms^-1

Haryana State Board HBSE 9th Class Science Important Questions Chapter 8 Motion Important Questions and Answers.

Haryana Board 9th Class Science Important Questions Chapter 8 Motion

Very Short-Answer Type Questions

Question 1.
What do you mean by rest ?
Answer:
When a body does not change its position with respect to its surroundings, then the body is said to be at rest.

Question 2.
What is meant by motion ?
Answer:
When the position of the body continuously changes with respect to its surroundings, then the body is said to be in motion.

Question 3.
What is meant by relative motion ?
Answer:
The increase or decrease in distance between two moving bodies is known as relative motion.

Question 4.
How the motion of air can be measured ?
Answer:
The motion of air can be measured by its effect.

Question 5.
Passengers are sitting in a moving train. Tell, about which objects the passengers are in rest position and about which objects the passengers are in motion ?
Answer:
A passenger sitting in a moving train is in the state of rest in comparison of other passengers and the luggage kept in train. But the same person is in motion as compared to outsider trees and buildings.

Question 6.
Give one difference betw een the motion of living and non-living things.
Answer:
Living organisms move by themselves but external factor is required for the motion of non-living things.

Question 7.
What is distance ?
Answer:
The total path travelled by a body between initial and final points is called distance.

Question 8.
What is displacement?
Answer:
The shortest distance between the initial and final position of the body is called displacement.

Question 9.
What is the SI unit of distance and displacement ?
Answer:
The SI unit of distance and displacement is metre.

Question 10.
What is meant by reference point or origin point ?
Answer:
A fixed point with respect of which a body is at rest or in motion is known as reference point or origin point.

Question 11.
What those quantities are called, which require magnitude and direction both for their expression ?
Answer:
Those quantities which require magnitude and direction both for their expression are called vector quantities.

Question 12.
Which quantities are expressed by magnitude only ?
Answer:
Scalar quantities are expressed by magnitude only.

Question 13.
Write two examples each of vector and scalar quantities.
Answer:
Vector quantities – Velocity and displacement.
Scalar quantities – Distance and speed.

Question 14.
When an object covers equal distance in equal intervals of time, then what its speed is called ?
Answer:
When an object covers equal distance in equal intervals of time, its speed is known as uniform speed.

Question 15.
Give two examples of uniform speed.
Answer:
(i) Motion of earth
(ii) Motion of pendulum of a watch.

Question 16.
When an object covers unequal distance in equal intervals of time, then what its speed is called ?
Answer:
When an object covers unequal distance in equal intervals of time, its speed is known as non¬uniform speed.

Question 17.
Write two examples of non-uniform speed.
Answer:
(1) Train starting from a station.
(2) Birds flying in the sky.

Question 18.
Write down the formula to find out the average speed of a moving object.
Answer:
The distance travelled by an object per unit time is known as average speed.

Question 19.
What is meant by velocity ?
Answer:
The distance covered by a moving body in one second in a certain direction is called velocity.

Question 20.
What is the unit of velocity ?
Answer:
The unit of velocity is metre per second (ms’1).

Question 21.
What is the relation among distance, speed and time ?
Answer:
Distance = Speed x Time

Question 22.
What will be the velocity of an athlete, if he takes 10 seconds to cover a distance of 100 metres ?
Answer:

Question 23.
What is meant by acceleration ?
Answer:
The rate of change of velocity of a moving body is called acceleration.
a = \(\frac {v – u}{t}\)

Question 24.
What is meant by retardation ?
Answer:
The rate of decrease in velocity in a certain direction is called retardation i.e. negative acceleration s called retardation.

Question 25.
What is SI unit of acceleration ?
Answer:
SI unit of acceleration is metre Der second sauare

Question 26.
Write example ot accelerated motion.
Answer:
A body moving in a circle with uniform speed is an example of accelerated motion.

Question 27.
Choose scalar and vector from following :
(i) Delhi is at a distance of 1450 km from Mumbai.
(ii) Delhi is at a distance of 1450 km in north from Mumbai.
Answer:
(i) It is an example of scalar quantity.
(ii) It is an example of vector quantity.

Question 28.
When, a body is said to be moving with uniform acceleration ?
Answer:
If there is equal change in velocity in equal intervals of time, then the body is said to be moving with uniform acceleration.

Question 29.
Define uniform circular motion.
Answer:
When a body moves in a circular path with uniform speed, its motion is known as uniform circular motion.

Question 30.
Which type of motion is shown, if the speed-time graph is a straight line ?
Answer:
It shows uniformly accelerated motion.

Question 31.
What will be the acceleration of the body, if the speed-time graph is parallel to time axis ?
Answer:
The speed of the body will uniform, therefore acceleration will be zero.

Question 32.
What shows the slope of speed-time graph of an object ?
Answer:
Acceleration of the object.

Question 33.
What the area under and between interval of speed-time graph of moving body shows ?
Answer:
The distance covered by the body in that time interval.

Question 34.
If the distance-time graph, parallel to time axis is a straight line, then average speed in different intervals will be equal or different.
Answer:
Equal.

Question 35.
If the distance-time graph of a body is a straight line, what you will say about the motion of the body ?
Answer:
The body will be in constant position.

Question 36.
If the distance-time graph of a body is a curve, then its average speed in different intervals will be different or uniform.
Answer:
The average speed will be different in different intervals.

Question 37.
If the speed of a moving body becomes 30 km/h from 0 in 2 hours, then what will be its acceleration?
Answer:
Acceleration =img= 15 kmh^-2

Question 38.
If a body is moving on circular track with uniform-speed, then which type of its motion will be ?
Answer:
Non-uniform and accelerate motion.

Question 39.
Speed of light is 3 x 10⁸ ms^-1. What will be its speed in kmh^-1 ?
Answer:
speed of light = 3 x 10⁸ms^-1 = \(\frac{3 \times 10^8 \times 3600}{1000}\)kmh^-1
= 1.08 x 10⁹kmh^-1

Question 40.
Rajdhani Express covers a distance of 1384 km in 17 hours. What will be its average speed?
Answer:

Question 41.
What will be the average speed of a car, if it covers a distance of 80 km in two hours ?
Answer:
Average speed = \(\frac {80}{2}\) = 40 kmh^-1

Question 42.
What is meant by circular motion ?
Answer:
When a body moves on circular track, its motion is known as circular motion.

Question 43.
Give two examples of circular motion.
Answer:
(1) The motion of the wheel of a vehicle.
(2) The motion of a stone tied on the end of a rope in plane circle.

Question 44.
What is meant by graph ?
Answer:
The figure representation of any information is called graph.

Question 45.
Which type of motion is shown by a freely falling object ?
Answer:
It shows a uniformly accelerated motion.

Question 46.
A stone is thrown in vertical direction, then its velocity is continuously decreasing. Why ?
Answer:
When a stone is thrown in vertical direction, its velocity continuously decreases because the acceleration due to gravity is always directed towards the centre of earth.

Question 47.
You have gone to school on 8 o’clock in morning and come back 2 o’clock in afternoon. What will be your displacement?
Answer:
Zero.

Question 48.
What will be the velocity of that object which is thrown vertically upward from the surface of earth and attains maximum height ?
Answer:
Zero.

Question 49.
What is the relation among s, u, a and t ?
Answer:
s = ut + \(\frac {1}{2}\) at².

Question 50.
What is the relation among v, u, a and t ?
Answer:
v = u + at

Question 51.
What is the relation among v, u, a and s ?
Answer:
v² – u² = 2as

Question 52.
What will be the speed of an athlete, when he completes a round in t seconds on a circular track of radius r ?
Answer:
Speed (v) = \(\frac {2πr}{t}\)

Question 53.
When there are clouds in the sky, the lightning and thundering happen in same time. First, you see the eightning After some time, the sound of thundering reaches to you. Can you tell, why it is so ?
Answer:
Because the velocity of light (3 x 10⁸ ms^-1) is much more than the velocity of sound (346 m/s).

Short Answer Type Questions

Question 1.
What is the difference between rest and motion ?
Answer:
When a body does not change its position with respect to its surroundings, it is called rest, e.g. a book lying on the table, a stone lying on the floor, etc. When the position of the body continuously changes with respect to its surroundings, it is called motion, e.g. a moving car, a running horse, etc.

Question 2.
What is meant by displacement ? When it is positive and negative ?
Answer:
The change in the position of body in a certain direction is called displacement.
The position of a body changes from x₁ to x₂, then the displacement (d) can be written as:
d = (x₂ – x₁)
The +ve and -ve signs of displacement shows the direction of change in position of body. If displacement is +ve, then body moves from left to right. If the displacement is -ve, then body moves from right to left. It is a vector quantity.

Question 3.
What is meant by speed ? Write its unit.
Answer:
Speed is the distance travelled by the body in unit time interval in any direction.

Suppose, a body covers a distance ‘s’ in time ‘ f, then its speed v = –
Unit of speed is metre per second (ms^-1). 1

Question 4.
What is meant by non-uniform motion ? Draw a graph for non-uniform motion.
Answer:
Motion of a body is said to be non-uniform, if it covers unequal distance in equal intervals of time, e.g. motion of a car on road, because its speed keeps on changing. Similarly, the motion of a train is an example of non-uniform motion, because train covers different distance in every second. Distance-time graph is shown to clear the motion of train. It is clear from the figure that speed changes with time and distance-time graph is not a straight line. It is an example of

Question 5.
How vector is shown ?
Answer:
Vector is represented by a straight line with an arrow head over it. The length of this line is proportional to the magnitude of vector and arrow head shows the direction, which is known as the ‘head’ of vector and other end is known as the ‘tail’ of vector. For example, a velocity of 30 ms^-1, 30° in south-west direction can be shown in the form of a line carrying arrow head, as shown in figure.

Question 6.
Two cars moving in opposite directions, cover an equal distance d in an hour. What will be displacement of each after an hour, if they are moving in north and south directions respectively ?
Answer:
Let O is the reference point of both cars.
The distance covered by car A from reference point O in hour in north direction = d
∴Displacement OA = d
The distance covered by car B from reference point O in hour in south direction = d
∴Displacement OB = d
Total displacement of both cars, AB = d + d = 2d

Question 7.
What is meant by graph ? What are its uses ?
Answer:
To draw the change in one physical quantity7 with respect to another physical quantity on two different axes is called graph.

Uses: The uses of graph are as follows:
(l) The relation among different quantities can be studied easily.
(2) The table of two or more than two quantities can be compared easily.
(3) It is more simple to explain quantity in graph than table.
(4) Graph represents data in less space in comparison to table which takes larger space to represent data.
(5) Quantity related to slope of graph can be found.

Question 8.
What is distance-time graph ? The distance covered by a bus in different time intervals is given in the table. Draw a distance-time graph with the help of it.

Answer:
A simple and successive method, which shows the different distances at different time of a moving body, is called distance-time graph. The distance covered by the bus in different time-intervals is shown in distance-time graph.

Question 9.
Draw distance-time graph for tw o bodies moving with uniform speed of 4 ms^-1 and 7 ms^-1 and compare it.
Answer:
We know that,
Distance = Speed x Time
(i) Distance-time graph for a body moving with uniform speed of 4 ms^-1.


(ii) Distance-time graph for a body moving with uniform speed of 7 ms^-1.

On drawing these values on graph paper, we see that distance-time graph of given body will be as the adjacent figure.

Comparison of Graphs:
The slope of the body moving with uniform speed of 7 ms^-1 will be more than that of the body moving with uniform speed of 4 ms^-1.

Question 10.
Distance-time graph for a body is shown in figure. Is it the graph of real situation ? Give reason.
Answer:
No, this is not the graph of real situation. Reasons are as follows:
(1) According to distance-time graph, the time taken to reach that point from where it started its journey is less than the time taken by it to complete that journey.
(2) Time (t) is such a quantity which is continuously increasing. This will be larger after t = 14.

Question 11.
Distance-time table of a moving car is as follows:

Draw distance-time graph for car on the graph paper. Answer: Distance-time graph for car:

Question 12.
The distances covered by Amitabh and Archna by their bicycles in different times:

Show both by distance-time graph.
Answer:
The distance-time graph for both is given below:

Question 13.
Draw velocity-time graph for a body moving with a constant velocity of 40 kmh^-1.
Answer:
To draw a velocity-time graph of a car moving with constant velocity’ of 40 kmh^-1. It means, car covers a distance of 40 km in an hour, 80 km in two hours, 120 km in 3 hours and so on, it can be seen from figure, that velocity-time graph is a straight line and parallel to time axis. It is true for all velocity-time graphs when motion is uniform.

Question 14.
How we can calculate the distance covered by a body in a given time by using velocity¬time graph ?
Answer:
Suppose the velocity-time graph of a car moving with speed of 40 kmh^-1 is as the given figure. Let us consider, we have to calculate the distance covered by the car between time and t₂. Draw perpendiculars from points t₁ and t₂ on time axis as shown in figure.

By this, we obtain a rectangle ABCD between graph and X-axis. In this rectangle side AD is equal to BC, which is equal to (t₂ -t₁), and side AB is equal to CD, which is similar to 40 kmh^-1. We know that, if a body moving with velocity (v) covers a distance (.s’) in time (?) then,
s = vt
∴ Distance covered by the car in time (t₂ – t₁) = [(40 kmh^-1) (t₂ – t₁)h]
= 40(t₂ – t₁) km
= Area of rectangle ABCD or the area under velocity-time graph shows the distance covered by the car. This is true for any velocity-time graph, whether velocity is uniform or non-uniform,

Question 15.
How velocity is calculated by straight-lined distance-time graph ? Explain.
Answer:
We can calculate the velocity of a car from its distance-time graph. In fig., think about the smaller part AB of distance-time graph of motion of car. We draw a straight-line from point A parallel to X-axis and from point B parallel to Y-axis to find the velocity of car. These two straight lines meet at a point C and make a AABC. Now, on graph, AC represents time-interval (t₂ – t₁), and BC is equal to distance (s₂ – s₁). It can be seen from the graph that when car move from point A to B, it covers a distance (s₂ – s₁) in time (t₂ – t₁)
Velocity of car = \(\frac{s_2-s_1}{t_2-t_1}\)

Question 16.
Show uniformly accelerated motion, non-uniformly accelerated motion and uniform retarded motion by graph.
Answer:
1. Uniformly Accelerated Motion: In uniformly-accelerated motion, speed-time graph is a straight a line.

2. Non-uniformly Accelerated Motion: In non-uniformly accelerated motion, speed-time graph is a

3. Uniformly Retarded Motion: In uniformly retardation, the acceleration is negative (-ve) and velocity time graph is a straight line.

Question 17.
Draw speed-time graph for a body, moving in a straight line. What the slope of this straight line show ?
Answer:
If there is equal change in the velocity of a body in equal intervals of time, then we can say that the body is moving with uniform acceleration. The speed-time graph for a body moving in a straight-line is shown in figure. If the speed of the body is v₁ at time t₁ and v₂ at time t₂, then
acceleration of the body, a = \(\frac{v_2-v_1}{t_2-t_1}\)

The time intervals (t₂ – t₁) and (t₄ -t₃) are equal as shown in figure, because the change in heights of speed are also equal. Therefore, this graph shows the motion of such a body, which is moving with uniform acceleration.
The speed-time graph of a body moving with uniform acceleration is a straight line. The acceleration of such body is the slope of this straight line.

Question 18.
How you will prove that the motion is relative ?
Answer:
In order to prove that the motion is relative, we can compare the passengers sitting in a moving bus or train with road or trees standing near the track, vehicle or persons, e.g. the passengers sitting inside the bus . or train are in rest as compared to the luggage lying inside, but are in motion as compared to outsided objects.

Question 19.
Write the difference between-
(i) vector and scalar.
(ii) uniform and non-uniform motion.
(iii) distance and displacement.
Answer:
The difference between vector and scalar:
Vector:
1. Those physical quantities which contains both direction and magnitude are known as vector quantities, e.g. velocity, displacement, force, etc.
2. Vector quantities are combined according to rule of triangle or parallelogram.
3. Vector quantities are represented by a straight line with an arrow head over it.

Scalar:
1. Those physical quantities which contain magnitude only is known as scalar quantities, e.g. distance, volume, mass, etc.
2. Scalar quantities can be combined algebraically.
3. There is no special method to represent scalar quantities.

(ii) The difference between uniform and non-uniform motion :
Uniform Motion:
When a body covers equal distance in equal intervals of time, its motion is called uniform motion, e.g. motion of earth, motion of pendulum of watch, the motion of moon around the earth.

Non-uniform Motion:
When a body covers unequal distance in equal intervals of time, its motion is called non¬uniform motion, e.g. motion of train starting from station, the motion of bus starting from bus stop, motion of cycle.

(iii) The difference between distance and displacement:

Distance:
1. The length of the path actually covered by the body is called distance.
2. It is a scalar quantity.
3. The distance between two points through different paths can be different.

Displacement:
1. The distance between the initial and final positions of the body is called displacement.
2. It is a vector quantity.
3. The value of the displacement between any two points is always same.

Question 20.
What is meant by uniform circular motion ? Justify your answer with example.
Answer:
When a body moves on circular track, it changes its direction at every point. Actually, circle is a polygon figure which has infinite sides. In figure any circular shaped track can be called a polygon of inner-sides. Therefore, a body moving in a circle with uniform speed is an example of accelerated motion. Although, there is no change in the speed of the body, but the direction of the motion of body is continuously changes. Example – Take a piece of thread and tie one stone on its one end and rotate it, it will be in a circular motion.

Numerical Questions

Question 1.
The distance between the home of a boy and school is 1.8 km, if he takes 5 minutes to reach school by cycle, then find his speed In metre/second.
Solution:
Distance (s) = 1.8 km = 1.8 x 1000 metres = 1800 metres
Time taken (t) = 5 minutes = 5 x 60 seconds = 300 seconds

= 6 ms^-1

Question 2.
A person takes 10 minutes to reach office from his home. If the office is at a distance of 3.6 km, then find the average speed of person.
Solution:
Total distance 3.6 km = 3.6 x 1000 m = 3600 metres
Total time = 10 minutes = l0 x 60seconds = 600 seconds
Total distance 3600 m

= 6 ms^-1

Question 3.
Trivendrum express moves from Guwahati at 23 : 30 hrs on Monday and after covering a distance of 3574 km, It reaches Trivendrum at 22 : 30 hrs on Thursday. Find out the average speed of
this train.
Solution:
The total distance covered by the train 3574 km
Total time between 23:30 hrs (Monday) to 22:30 hrs (Thursday) = 24 + 24 + 23 – 71h

= 50.34 kmh^-1

Question 4.
A car, starting from rest, acquire a velocity of 36 kmh’ in 10 seconds. Find out acceleration of the car.
Solution:
The car started from rest
∴ Initial velocity (u) = O
Final velocity (v) = 36 kmh^-1 = 36 x \(\frac {5}{18}\) = 10 ms^-1
Time (t) = 10 s
We know that. v = u + at
10 = 0 + a x 10
10 = 10 a
a = \(\frac {10}{10}\) = 1 ms^-1

Question 5.
A cycle moving with a velocity of 3 metre per second increase its motion with acceleration of 0.5 ms² . What will be Its velocity after 5 seconds and how much distance it will cover ¡n this time?
Solution:
Here, Initial velocity (u) = 3 ms
Acceleration (a) = 0.5 ms²
Time (t) = 5 s
Final velocity (v) = ?
Distance (s) = ?
We know that,
v = u + at = 3 + 0.5 x 5 = 3 + 2.5 = 5.5 ms^-1

(2) s = ut+ \(\frac {1}{2}\) at²
= 3 x 5 + \(\frac {1}{2}\) x 0.5 x 5 x 5
15 + 6.25 = 21.25 m

Question 6.
The uniform acceleration of a scooter is 4 ms2. How much distance will scooter cover after 10 seconds from its movement ? What will be its velocity after 10 s?
Solution:
Here,
Initial velocity of scooter (u) = 0
Acceleration (a) = 4 ms
Time (t) = 10 s
Distance (s) = ?
Final velocity (y) = ?
We know that
(1) s = ut + \(\frac {1}{2}\) at²
s = 0 x 10 + \(\frac {1}{2}\) x 4 x (10)²
s = 0 + \(\frac {1}{2}\) x 4 x 100 = 200m
(2) v = u + at = 0 + 4 x 10 = 40 ms^-1

Question 7.
A bicycle is travelling at a speed of 10 ms. The brakes are applied so as to produce a retardation of 0.5 ms2. Find, how far the bicycle travel before it is brought to rest?
Solution:
Initial velocity of bicycle (u) = 10 ms^-1
Final velocity (v) = 0
Retardation (a) = 0.5 ms^-2
We know that, v² – u² = 2as
(0)² – (10)² = 2(- 0.5) x s
– 100 = – 1s
s = 100 m

Question 8.
A car travels with uniform velocity 20 ms’ for 5 s. On applying brakes, the car comes to rest in 8s with uniform retardation. Draw, velocity-time graph. How far, the car will go after applying brakes?
Solution:
The velocity-time graph is shown in figure.
The distance covered by the car, after applying brakes
= area of ∆BDC = \(\frac {1}{2}\) x DC x DB
[ ∴ area of triangle = \(\frac {1}{2}\) x base x perpendicular]
= \(\frac {1}{2}\) x (13 – 5) x 20
= \(\frac {1}{2}\) x 8 x 20 = 80 m.

Question 9.
In a long running, the athletes have to move 4 rounds of running track The starting and end of race is at the same place. If the length of one round is 200 m then –
(a) how much distance is to be covered by athletes?
(b) what will be the total displacement when the athletes has completed the race?
(c) is the motion of athletes uniform or non-uniform?
(d) are the distance covered by the athletes and displacement equal, at the end of race?
Answer:
(a) The total distance to be covered by the athletes = 200 x 4 = 800 metres.
(b) Because the initial and final places of running track are at same place, therefore the total displacement of athletes = zero.
(c) The motion of athletes is non-uniform.
(a) The distance covered by the athletes at the end of race is not equal to displacement. Because –
Distance = 800 metres
Displacement = 0

Question 10.
Write the speed of following bodies in descending order –
(i) Bicycle running with a speed of 18 kmh^-1.
(ii) An athlete running with a speed of 7 ms^-1.
(iii)A car running with a speed of 2000 m min^-1
Solution:
We know that,
(i) 18 kmh^-1 = \(\frac {18000}{3600}\) ms^-1 = 5 ms^-1
(ii) 7 ms^-1
(iii) 2000 m min^-1 = \(\frac {2000}{60}\) ms^-1 = 33.33 ms^-1
∴ The descending order of speed of bodies is as follows:
(i) A car running with a speed of 2000 m min^-1.
(ii) An athlete running with a speed of 7 ms^-1.
(iii) A bicycle running with a speed of 18 kmh^-1.

Question 11.
A body moves with velocity of 2 ms^-1 for 5 seconds, in next 5 seconds, its velocity increases to 10 ms^-1 due to uniform acceleration. After that, its velocity decreases uniformly and comes in rest in 10 seconds, then
(a) draw velocity-time and distance-time graphs for the motion of the body.
(b) Show that portion in graph, where the motion is uniform and non-uniform.
(c) From graph, find the distance covered by the body after 2s and 12s and in the last lOs.
Answer:
(a) Velocity-time graph: The velocity of the body is 2 ms for first 5 seconds, which is marked
by AB in the graph. After that, it becomes 10 mst in another 5 seconds (between 5 and 10 s), which is marked
by BC in the graph. After that the body comes in rest in next 10 seconds, which is marked by CD in the graph.

(b) Distance-time graph: Because the speed of the body is not uniform. Therefore, distance-time graph is not a straight-line

From velocity-time graph, we find that the motion of the body is uniform in AB part, whereas the motion is non-uniform in BC and CD parts.
(c) (1)The distance covered by the body in 2s = 2 x 2 = 4 m.
(2) The distance covered by the body in 12 s = area of [OB’BA + BBC’C + CC’FF’]
Now, the area of rectangle OBBA = 2 x 5 = 10
Area of trapezium BB’C’C = \(\frac {1}{2}\) x (BB’ + CC’) x B’C
= \(\frac {1}{2}\) (2 + 10) x 5
= \(\frac {1}{2}\) x 12 x 5 = 30
Area of trapezium CC’FF’ = 4- (CC’ + FF’) x CF’
= \(\frac {1}{2}\) x (10 + 8) x 2 = \(\frac {1}{2}\) x 18 x 2 = 18
∴ The distance covered by the body in 12 sec 10 + 30 + 18 = 58 metres

(3) Distance covered in last lO seconds area of (trap. CC’ F’F + right-angle ∆FF’D
Now, area of trapezium CC’F’F = x (CC + FF’) x C’F’
= \(\frac {1}{2}\) x (10 + 8) x 2
= \(\frac {1}{2}\) x 18 x 2 = 18

Area of right-angle ∆FF’D = \(\frac {1}{2}\) x F’D x F’F = \(\frac {1}{2}\) x 8 x 8 = 32
∴ Distance covered in last 10 seconds = 18 + 32 = 50 metres.

Do Yourself

1. Rita takes 20 minutes to cover a distance of 3.2 km on a bicycle. Calculate her velocity in units of a kilometre minute and kilometre/hour.
Answer:
0.16 km/minute, 9.6 km/hour

2. Ahmed is driving his car with a velocity of 45 kmh^-1. How much distance will be covered in
(a) one minute and
(b) one second?
Answer:
(a) 750 metres
(b) 12.5 metres

3. Starting from rest, Saurabh paddles his bicycle to attain a velocity of 6 ms^-1 in 30 seconds. Then, he applies brakes after that the velocity of the bicycle comes down to 4 ms^-1 in next 5 seconds. Calculate the acceleration of the bicycle in both the cases.
Answer:
(a) 0.2 ms^-2
(b) -0.4 ms^-2

4. A train starting from rest attains a velocity of 108 kmh^-1 in 10 minutes. Calculate (I) acceleration (ii) distance covered by the train.
Answer:
(1) 0.5 ms²
(ii) 900 m

5. A train starting from rest attains a velocity of 72 kmh^-1 in 5 minutes. Assuming that the acceleration is uniform, find (j) acceleration of train and (ii) the distance travelled by the train while it attained this velocity.
Answer:
(i) ms^-2
(ii) 3 km

6. A car accelerates uniformly from 18 kmh^-1 to 36 kmh^-1 in 5 seconds. Calculate : (1) the acceleration and (ii) the distance covered by the car in that time.
Answer:
(i) 1 ms^-2
(ii) 37.5 m

7. The brakes applied to a car produces a negative acceleration of 6 ms2. if the car takes 2 seconds to stop after applying the brakes, calculate the distance it travels, during this time.
Answer:
12 m

8. A train covers a distance of first 30 km out of 60 km lengthy path with a uniform speed of 45 kmh^-1. By how much speed, the train will cover the remaining 30 km path so that its average speed will be 60 kmh^-1 ?
Answer:
90 kmh^-1

9. Choose right answer out of the following questions:
(a) How much distance will a car cover in 12 minutes moving with a speed of 35 kmh^-1’?
(i) 7 km
(ii) 35 km
(iii) 14 km
(iv) 28 km
Answer:
(i) 7 km

(b) If, the acceleration of the body moving with a speed of 20 ms^-1 in a straight line ¡s 4 ms^-2, then
how much speed of it will be after 2 seconds?
(1) 8 ms^-1
(ii) 12 ms^-1
(iii) 16 ms^-1
(iv) 28 ms^-1
Answer:
(iv) 28 mst

(C) The speed of a car becomes 50 kmh^-1 from 20 kmh^-1 in 10 seconds. The acceleration of this car is –
(i) 30 ms²
(ii) 3 ms²
(iii) 1 8 ms²
(iv) 0.83 ms²
Answer:
(iv) 0.83 mc²

10. A piece of wood slides down from rest on plane of 10m tong with an acceleration of 5 ms² . What will be the speed of piece of wood on reaching at the base of inclined plane?
Answer:
10 m /s

11.. A train is travelling at a speed of 90 kmh^-1 On applying brakes, a retardation of 0.5 mc² s produced. Find how far the train goes before it is brought to rest?
Answer:
625 m

12. A body covers a distance of 16 metres in 4 seconds and again covers a distance of 16 metres in 2 seconds. What will be the average speed of body?
Answer:
5.33 ms^-1

13. The odometer of a car represents 2000 km at the start of a trip and 2400 km at the end of the trip. If the trip took 8 hours then, calculate the average speed of the car in kmh’ and ms.
Answer:
50kmh^-1, 13.9 ms^-1

14. Usha swims in a 90 m long pool. She covers 180 m in one minute by swimming from one end to the other and back along the same straight path. Find the average speed and average velocity of Usha.
Answer:
Speed 3 ms^-1, Velocity = O ms^-1

15. Starting from a rest position, Rahul paddles his bicycle to attain a velocity of 6 ms1 in 30s. Then he applies brakes such that the velocity of bicycle comes down to 4 ms^-1 in the next 5s. Calculate the acceleration of the bicycle ¡n both the cases.
Answer:
0.2 m² 0.4 ms

Essay Type Question

Question 1
Prove the following equations:
(i) v = u + at²
(ii) s = ut + ut²
(iii) v² – u² = 2as
Solution:
(i) Let the initial velocity of the body = u
Time = t
Final velocity = v
Change in velocity = v – u
Rate of change in velocity (acceleration), a = \(\frac {v – u}{t}\)
at = v – u
at+u = v
v = u + at
Let the initial velocity of the body = u
Acceleration = a
and after time t, final velocity = v
1f after t sec, the distance is s, then distance (s) = average velocity x time
But, average velocity = \(\frac {v – u}{t}\)
∴Distance (s) = \(\frac {v – u}{t}\)
s = \(\frac {v – u}{2}\) x t
s = \(\frac {u + u + at}{2}\) x t [∴v = u + at]
s = \(\frac {2u + 2t}{2}\) x t
s = \(\left(\frac{2 u t+a t^2}{2}\right)=\frac{2 u t}{2}+\frac{a t^2}{2}\)
s = ut + \(\frac {1}{2}\) at²

(iii) We know that, v = u + at
Squaring both sides
(v)² = (u + at)²
v² = u² + a²t² + 2uat
v² – u² = a²t² + 2uaI
v²– u² = 2uat + a²t²

v²– u² = 2a(ut + \(\frac {1}{2}\) at²)
v²– u² = 2as

Practical Work

Experiment 1:
Describe one activity for the difference between distance and displacement.

Procedure:
Take a metre scale and a long rope. Walk from one corner of a basket-ball court to its opposite corner way and measure with the help of scale. This will be the distance covered by you, whereas you will get displacement by putting a straight-rope from one corner to another. Suppose ABCD is basket-ball court. Distance to go from A to C AB + BC, whereas displacement = AC.

Experiment 2:
Clarify with an activity that direction of motion changes at every point on circular track

Procedure:
Take a piece of thread and tie a small piece of stone at one of its ends, move the stone to describe a circular path with constant speed by holding the thread at the other end as shown in figure. Now, let the stone go by releasing with thread and measure the direction of stone.

By repeating the activity for a few times and releasing the stone at different positions of circular path, check whether the direction in which the stone moves remains the same or not If you carefully note, on being released the stone moves along a straight line tangential to the circular path. This is because once the stone is’ released, it continues to move along the direction it has been moving at that instant. This shows that the direction of mot ion changes at every point when the stone was moving along the circular path.

Quick Review of the Chapter

1. A train is moving. The passengers sitting inside it, are ¡n rest compared to :
(A) other passengers
(B) the luggage in the train
(C) outsider objects
(D) other passengers and luggage in train
Answer:
(D) other passengers and luggage ¡n train

2. A train is moving. The passengers sitting inside it, are in motion as compared to :
(A) other passengers
(B) the luggage in the train
(C) outsider buildings and trees
(D) other passengers and luggage in train
Answer:
(C) outsider buildings and trees

3. If any object changes its position continuously with respect to other object, then objett is in state of
(A) motion
(B) rest
(C) constant
(D) none of these
Answer:
(A) motion

4. If any object does not change its position with respect to its surroundings, then the object is in state of
(A) motion
(B) rest
(C) circular motion
(D) movement
Answer:
(B) rest

5. Which of the following moves by themselves?
(A) living things
(B) non-living things.
(C) both living and non-living things
(D) neither living nor non-living
Answer:
(A) living things

6. SI unit of distance is:
(A) km
(B) m
(C) cm
(D) mm
Answer:
(B) m

7. WhIch of the following is a scalar quantity?
(A) momentum
(B) velocity
(C) displacement
(D) distance
Answer:
(D) distance

8. Rate of change of velocity is known as:
(A) Speed
(B) Acceleration
(C) Momentum
(D) Force
Answer:
(B) Acceleration

9. When a body covers equal distance in equal intervals of time, it is said to be
(A) uniform speed
(B) non-uniform speed
(C) average speed
(D) accelerated motion
Answer:
(A) uniform speed

10. If acceleration is in the direction of velocity, then it is called:
(A) Negative acceleration
(B) zero acceleration
(C) Positive acceleration
(D) none of these
Answer:
(C) Positive acceleration

11. If acceleration is ¡n the opposite direction of velocity then it is called:
(A) Negative acceleration
(B) zero acceleration
(C) positive acceleration
(D) none of these
Answer:
(A) Negative acceleration

12. If an object moves ¡n a circular path with uniform speed, Its motion is called: [H.B.S.E. 2020]
(A) Uniform circular motion
(B) Non-uniform circular motion
(C) Uniform curved motion
(D) Non-uniform curved motion
Answer:
(A) Uniform circular motion

13. SI unit of speed Is: [H.B.S.E. March, 2019]
(A) ms^-2
(B) ms^-1
(C) kmh^-1
(D) kms^-1
Answer:
(B) ms^-1

14. The distance covered by a moving body in one second in a certain direction is called:
(A) velocity
(B) acceleration
(C) non-uniform speed
(D) uniform speed
Answer:
(A) velocity

15. What is the relation among distance, speed and time?
(A) distance x speed = time
(B) time x distance = speed
(C) distance speed x time
(D) none of these
Answer:
(C) distance = speed x time

16. What will be the velocity of athlete if he takes 10 s to cover a distance of 100m?
(A) 100 ms^-1
(B) 10ms^-1
(C) 10 ms^-2
(D) 10 ms^-2
Answer:
(B) 10 ms^-1

17. The rate of decrease In velocity in a certain direction is:
(A) +ve acceleration
(B) – ve acceleration
(C) +ve and – ve acceleration
(D) none of these
Answer:
(B) – ve acceleration

18. The downward slope in velocity-time graph shows:
(A) accelerated motion
(B) equal motion
(C) retarded motion
(D) none of these
Answer:
(C) retarded motion

19. Rajdhanl Express covers a distance of 1384 km in 17 hours. Its average speed will be:
(A) 81.4 ms^-1
(B) 81.4 kms^-1
(C) 81.4 mh^-1
(D) 81.4 kmh^-1
Answer:
(D) 81.4 kmlf1

20. If a car covers a distance of 80 km in 2 hours, then its average speed will be:
(A) 40 kmh^-1
(B) 40 kms^-1
(C) 40 ms^-1
(D) 40 mh^-1
Answer:
(A) 40 kmh^-1

21. Cheetah is the fastest land animal and can achieve a peak velocity of 100 kmh upto a distance less than 500 m. H the cheetah spots his prey at a distance of 100 m, what ¡s the minimum time it will take to get the prey, if the average velocity attained by ¡t ¡s 90 kmh?
(A) 3s
(B) 4s
(C) 5s
(D) 6s
Answer:
(B) 4 s

22. The distance-time graph of a body is parallel to X-axis. It shows that:
(A) body is moving with non-uniform motion
(B) body is moving with accelerated motion
(C) the body is at rest
(D) body is moving with uniform motion
Answer:
(C) the body is at rest

23. By converting the speed of 2 km/h in m/s, we will get:
(A) \(\frac {5}{36}\) m/s
(B) \(\frac {5}{18}\) m/s
(C) \(\frac {5}{9}\)m/s
(D) \(\frac {50}{9}\) m/s
Answer:
\(\frac {5}{9}\)m/s

24. What is the speed of light in:
(A) 3 x 10⁸ m/s
(B) 3 x 10⁷ m/s
(C) 3 x 10¹⁰
(D) 3 x 10⁵ m/S
Answer:
(A) 3 x 10⁸ m/s

25. Which of the following is right for displacement?
(A) it cannot be zero
(B) its magnitude is more than the distance covered by the body
(C) it can be zero
(D) none of these
Answer:
(C) it can be zero

26. The odometer of any vehicle shows
(A) speed
(B) velocity
(C) distance
(D) time
Answer:
(A) speed

27. When an object Is In uniform motion, its path seems to be
(A) straight line
(B) curve
(C) irregular
(D) circular
Answer:
(A) straight line

28. During an experiment, a wireless signal from a spaceship reached ground station in 5 seconds. What Is the distance of spaceship from the ground station?
(A) 9 x 10¹⁰kjn
(B) 9 x 10¹⁰m
(C) 9 x 10¹⁰cm
(D) 9 x 10¹⁰ mm
Answer:
(B) 9 x 10¹⁰ m

29. A train is moving with a speed of 90 kmh^-1, on applying brakes, it produces a retardation of 0.5 ms². How much distance will it cover before coming to rest?
(A) 62.5 m
(B) 6.25 m
(C) 625 m
(D) 625 km
Answer:
(C) 625 m

30. A trolley while going down an inclined plane has an acceleration of 0.2 ms^-2. What will be its velocity In 3s after the starts?
(A) 0.6 ms^-1
(B) 0.6 cms^-1
(C) 0.6 mms^-1
(D) 0.6 ms^-2
Answer:
(A) 0.6 ms^-1

31. A racing car has a uniform acceleration of 4 ms^-2. What distance will it cover in lOs after the
start from rest?
(A) 20m
(B) 200m
(C) 2000m
(D) 2m
Answer:
(B) 200 m

32. A stone is thrown in vertically upward direction with a velocity of S ms⁴. If the acceleration of the stone during its motion is 10 ms², in downward direction, what will be the height aftalned by the stone?
(A) 12.5m
(B) 125m
(C) 1.25m
(D) 0.125m
Answer:
(C) 1.25 m

33. A stone Is thrown in vertically upward direction with a velocity of 5 ms. If the acceleration of the stone during its motion is 10 mr2, in downward direction, how much time will ¡t take to reach at maximum height?
(A) 0.5s
(B) 5s
(C) 5 min
(D) 0.5 mm
Answer:
(A) 0.5 s

34. An artificial satellite Is moving in a circular orbit of radius of 42,250 km. What will be Its speed, if it takes 24 hours to revolve round the earth?
(A) 3.07 ms^-1
(B) 3.07 kmh^-1
(C) 3.07 kms^-1
(D) 3.07 cms^-1
Answer:
(C) 307 kms^-1

35. An athlete completes one round of a circular track of radius r in time t, then its speed will be:
(A) 2πrt
(B) \(\frac{2 \pi r}{t}\)
(C) \(\frac{t}{2 \pi r}\)
(D) none of these
Answer:
(B) \(\frac{2 \pi r}{t}\)

36. The proper relation among s, u, t land a is:
(A) s = \(\frac{2 \pi r}{t}\)
(B) s = u + at
(C) s = ut + \(\frac {1}{2}\) at²
(D) s = uv + at
Answer:
(C) s = ut + \(\frac {1}{2}\) at²

37. The relation among y, u, a and t ¡s:
(A) v = u – at
(B) v = u + at
(C) v² = u² – at
(D) v² = u² + at
Answer:
(B) v = u + at

38. The proper relation between y, u, a and s is:
(A) v²= u² – 2as
(B) v² = 2as – u²
(C) v² – u² = 2as
(D) v² + u² = as
Answer:
(C) v² – u² = 2as

Haryana State Board HBSE 9th Class Science Important Questions Chapter 7 Diversity in Living Organisms Important Questions and Answers.

Haryana Board 9th Class Science Important Questions Chapter 7 Diversity in Living Organisms

Very Short-Answer Type Questions

Question 1.
Define Taxonomy.
Answer:
Science of classification of organism is known as Taxonomy.

Question 2.
Who classified the animals on the basis of their habitat ?
Answer:
Greek thinker Aristotle classified the animals into different groups based upon their habitat and habits.

Question 3.
Which type of cells have nucleus, cell organelles and cell wall ?
Answer:
Eukaryotic cells.

Question 4.
In which cell have the capacity to produce multicellular organisms ?
Answer:
Cell with nucleus.

Question 5.
Name the principle due to which some cell group together to form a single organism.
Answer:
Division of labour.

Question 6.
What are plants ?
Answer:
The organisms which produce their own food (autotrophs) are called plants.

Question 7.
What are animals ?
Answer:
The organisms which are heterotrophic known as animals.

Question 8.
Who proposed the concept of evolution ?
Answer:
Charles Darwin in his book “The Origin of Species” in 1859.

Question 9.
Which are primitive or lower organisms ?
Answer:
The group of organisms still possess their ancient body on earth is known as primitive or lower organisms.

Question 10.
Which are advanced or higher organisms ?
Answer:
The group of organisms who have undergone lot of changes in their body are called advanced or higher organisms.

Question 11.
Name the biologists who classified kingdom of organisms into broad categories.
Answer:
Ernst Haeckel (1894), Robert Whittaker (1959) and Carl Woese (1977).

Question 12.
What is the name of classification proposed by Whittaker ?
Answer:
Five kingdoms.

Question 13.
Which biologist classified the Monera Kingdom into Archaebacteria and Eubacteria ?
Answer:
Carl Woese.

Question 14.
Define species.
Answer:
Species is a group of organisms that are capable of breeding amongst themselves so as to produce fertile young ones. It is the smallest unit of classification.

Question 15.
What is the basic unit of classification ?
Answer:
Species.

Question 16.
What is nomenclature ?
Answer:
The system of naming animals and plants is termed as nomenclature.

Question 17.
Who is the father of Taxonomy ?
Answer:
Carolus Linnaeus.

Question 18.
Why does system of writing scientific names called bionomial system ?
Answer:
In this system every organism is given two names. One name is generic and the other is specific name.

Question 19.
What is the scientific name of human ?
Answer:
Homo sapiens.

Question 20.
What is the International System of nomenclature?
Answer:
Binomial system.

Question 21.
What are different categories of classification ?
Answer:
Species, Genus, Family, Order, Class, Phylum and Kingdom.

Question 22.
What is Genus ?
Answer:
Similar species together form genus.

Question 23.
How many kinds of kingdoms classified the living world in ancient time ?
Answer:
Two kingdoms:
(i) Plantae
(ii) Animalia.

Question 24.
What is classification ?
Answer:
Arranging of organism into groups on the basis of similarities and dissimilarities, which also show their relationship is called classification.

Question 25.
Write an importance of classification.
Answer:
It makes the study of organisms easy.

Question 26.
Which scientist classified the all organisms of the world into plantae and animalia kingdoms?
Answer:
Carolus Linnaeus in 1758.

Question 27.
Who raised the third kingdom Protista?
Answer:
E.H. Haeckel in 1866.

Question 28.
Who proposed the fourth kingdom Monera and fifty kingdom Animalia ?
Answer:
Robert H. Whittaker in 1969.

Question 29.
Which is the living organisms grow in whole life ?
Answer:
Plants.

Question 30.
How many sub-kingdoms of plant kingdom divided by Eichler ?
Answer:
Two: Cryptogamae and Phanerogamae.

Question 31.
Fungi cannot prepare their own food. Why ?
Answer:
Because chlorophyll is not present in them.

Question 32.
How many types of Angiosperms ?
Answer:
They are of two types:
(i) Dicot plants
(ii) Monocot plants.

Question 33.
Give two examples of Gymnosperms.
Answer:
(i) Cycas
(ii) Pinus.

Question 34.
Give one difference between algae and fungi.
Answer:
Chlorophyll present in algae but absent in fungi.

Question 35.
What is lichen?
Answer:
The symbiotic relationship of algae with fungi is called lichen.

Question 36.
Which sub-group of Cryptogams related to fungi ?
Answer:
Thallophyta.

Question 37.
Give one example of bryophyta.
Answer:
Mosses.

Question 38.
Give one example of pteridophyta.
Answer:
Ferns.

Question 39.
What are cryptogams ?
Answer:
The plants which do not bear seeds and spores located in their sex orgAnswer:

Question 40.
What is phanerogams ?
Answer:
Those plants in which seeds are produced after reproduction are called phanerogams.

Question 41.
What is meant by gymnosperms ?
Answer:
The plants bear naked seeds are called gymnosperms.

Question 42.
What is meant by angiosperms ?
Answer:
The plants which bear seeds into the fruit is called angiosperms. .

Question 43.
What is the main feature of plantae ?
Answer:
They are autotrophic.

Question 44.
What is the main feature of Animalia ?
Answer:
Heterotrophic.

Question 45.
What is porifera ?
Answer:
Those animals which bear pores all over their body are known as porifera.

Question 46.
Give two examples of coelenterata.
Answer:
Hydra and sea anemone.

Question 47.
What is the name of flatworm ?
Answer:
Platyhelminthes.

Question 48.
What is the scientific name of tapeworm ?
Answer:
Taenia solium.

Question 49.
Which group of animals is heterotrophic ?
Answer:
Nematoda.

Question 50.
Give one example of annelida.
Answer:
Earthworm.

Short-Answer Type Questions

Question 1.
What is the science of Taxonomy and Classification ?
Answer:
Taxonomy:
The branch of biology in which organisms are classified is called Taxonomy. First of all D. Candolli used this word Taxonomy involves identification, nomenclature and classification of organisms.

Classification:
It arranges the organisms in groups or set on the basis of their relations. Animals and plants are ranked in different categories as follow: Phylum, Class, Order, Family, Genus and Species. First of all, Carolus Linnaeus (1707-1778) gave idea about it in his book ‘Systema Naturae Therefore, Carolus Linnaeus is known as father of Taxonomy.

Question 2.
Why is it necessary to classify the living organisms ? Explain in your own words.
Answer:
The number of organisms in the world is very large. These organisms possess some similarities and some dissimilarties. The structure of some organisms is simple and that of others is complex. The organisms differ in their structure, nature, life-cycle, nutrition, respiration and reproduction, etc. Therefore, so as to make their study convenient, their classification is essential. The organisms are classified on the basis of similarities and dissimilarities. The science of classifiation provides a base for other branches of biology.

Question 3.
What is classification ? Explain its importance.
Answer:
Grouping organisms on the basis of similarities, dissimilarities and their inter-relationships is called classification.

Importance:
(1) Classification gives a base to the other branches of biology.
(2) Classification makes the study of organisms easy and convenient.
(3) Classification provides a clear picture of organisms.
(4) It provides information about inter-relationship of organisms.
(5) The study of geography is completely based on classification of plants and animals.
(6) The classification of organisms also contributes to the development of knowledge in other subjects.
(7) The branches of biology like ecology, cell biology, etc. have developed due to science of classification.

Question 4.
What is binomial nomenclature ? Explain with an example.
Answer:
Binomial Nomenclature: This system of nomenclature was given by Carolus Linnaeus. According to this system 4200 species of animals were named and were published in a book ‘SystemaNaturae’in 1758. In this system each plant or animal is given two names : The first name indicates the genera and is known as generic name whereas the second name indicates the specific name or species. Linnaeus is known as the father of Taxonomy.

For Example:
the scientific name of mango is Mangifere indica, that of mustard is Brassica compestris and that of man is Homo sapiens.
In all these the first name is generic name and the second name is that of species. All these names are universal and are used throughout the world.

Question 5.
What are the salient features of two kingdom system of classification ? Why are bacteria and fungi classified along with plants ?
Answer:
The living organisms are generally classified into two kingdoms : kingdom Animalia and kingdom Plantae. In both these kingdoms the characteristic features of organisms are same but they still differ in some characters. The organisms belonging to kingdom animalia are motile and cannot prepare their own food as they lack chlorophyll.

On the other hand the organisms belonging to kingdom plantae are (generally) autotrophs and prepare their own food. They are non-motile and remain confined to the same place. Their cell wall is made up of cellulose. They contain chlorophyll and are green. Bacteria and fungi do not contain green coloured pigment called chlorophyll, so they are not autotrophs. These obtain food/nourishment from dead or living organisms.

Still they are classified along with plants (kingdom Plantae) because:
(1) Their cell wall is made up of cellulose.
(2) They obtain their food/nourishment in soluble form.

Question 6.
Describe the different categories of classification ?
Answer:
Categories of the classification are the following:

Question 7.
What is Cryptogamae and Phanerogamae ?
Answer:
1. Cryptogamae: They are lowest group of plants. They lack flowers and seeds plants. They have bidden reproductive sex orgAnswer: Asexual reproduction takes place by the formation of spores.

2. Phanerogamae: They are highest group of plants. They bear roots, stem, leaves, flower, fruit and ’ seeds. They reproduce sexually by means of seeds. The seed contains embryo and nourishing material.

Question 8.
How is cryptogamae classified ?
Answer:
They are flowerless plants. Reproductive organs are hidden in them. There is no external flower and seed consists in them. According to classification, by Lindale and Eichler, cryptogamae is divided into three main groups:
(i) Thallophyta; e.g. Ulothrix, Penicillium, Lichens, etc.
(ii) Bryophyta; e.g. Funaria, Marchantia, etc.
(iii) Pteridophyta; e.g. Ferns, Selaginella, etc.

Question 9.
What is the difference between monocot and dicot plants ?
Answer:
These are the following differences between monocot and dicot plants :
Monocots:
1. Seeds with one cotyledon.
2. The leaves of these plants have parallel veination.
3. The root system is fibrous in them.
4. There is no secondary growth.
5. Stem divided into nodes.
Example: Wheat, maize, bajra, etc.

Dicots:
1. Seeds with two cotyledons.
2. Veination in their leaves is reticulate with a network of veins.
3. Tap root system is present in them.
4. Secondary growth is present.
5. Stem is not divided into nodes.
Example: Mustard (sarson), pea, gram, etc.

Question 10.
What is animalia ? Write names of main phylum and important features of this group. Answer: Animalia : The multicellular organisms with lack cell wall are called animalia. Their important features are following :
(i) They are heterotrophic and autotropic.
(ii) Their growth is definite.
(iii) These are free moving organisms.

They can be classified in the following :
(i) Porifera
(ii) Coelenterata
(iii) Platyhelminthes
(iv) Nematoda
(v) Annelida
(vi) Arthropoda
(vii) Mollusca
(viii) Echinodermata
(ix) Protochordata
(x) Vertebrata

Question 11.
Describe main features of porifera phylum.
Answer:
The main features of porifera are following:
(i) They mostly occur in saline water although some are found in fresh water.
(ii) They are multicellular.
(iii) Cells in them are loosely held together. Thus, they have cellular level of organisation.
(iv) Skeleton is not found in them.
(v) The shape of their body is the vase or sac like.
(vi) They bear pores all over body, with simple large opening known as osculum on the top.
(vii) They possess a unique canal system.
(viii) They reproduce by asexual and sexual methods.
Example:
Sycon, Spongia, Euplectella, Spongilla, etc.

Question 12.
Describe main features of Coelenterata.
Answer:
The main features of Coelenterata is following:
(i) They are solitary or colonial.
(ii) Anus is absent in them.
(iii) They possess radial symmetry.
(iv) They possess coelenterata.
(v) They bear tentacles.
(vi) Their body have stinging cells called cnidoblasts.
(vii) Polyp and medusa come into their life cycle one by one.
(viii) Reproduction is usually asexual in polyp form and sexual in the medusa form Examples : Hydra, Obelia, Sea anemone, Coral, etc.

Question 13.
Describe the main features of platyhelminthes.
Answer:
Platyhelminthes are characterised by the following main features:
(i) They are often dorso ventrally flattened.
(ii) They are usually endoparasites.
(iii) They are triploblastic, the body develops from three layers.
(iv) Their body having bilateral symmetry.
(v) Sexual reproduction takes place in them.
(vi) Only one hole is present in the alimentary canal.
(vii’) They have dorsoventrally flat and leaf like or ribbon like body.
Examples:
Tapeworm, planaria, liver- fluke, etc.

Question 14.
Write the main features of the nematoda phylum.
Answer:
Following are the main features of nematoda phylum:
(i) They are endoparasites.
(ii) They possess bilateral symmetry.
(iii) Alimentary canal is complete.
(iv) They are pseudocoelomates. Body cavity is not a true coelom in them.
(v) They are unisexual.
(vi) They are triploblastic.
(vii) Body size is microscopic and other are several centimetres in length.
Examples: Ascaris, Roundworm, Pinworm, etc.

Question 15.
Write main features of annelida phylum.
Answer:
Annelida phylum are characterised by the following main features:
(i) They live in moist soil, in freshwater or saline water.
(ii) They have long and palpented body.
(iii) They are first animals with true body- cavity or coelom.
(iv) Nephridia is present in them for the purpose of excretion.
(v) Animals have bilateral symmetry.
(vi) They are unisexual or bisexual.
(vii) Some forms have unjointed locomotary appendages, the parapodia. Others have setae for locomotion.
Examples: Earthworm, leech, nereis, sea mouse, etc.

Question 16.
What are the main features of arthropoda ?
Answer:
Arthropoda is characterised by the following main features :
(i) They occur everywhere, on land, in soil, in fresh and saline water.
(ii) They are heterotrophic.
(iii) They possess jointed legs.
(iv) Their body is segmented and divided into three regions: head, thorax and abdomen.
(v) Interior part of the body forms the distinct head, which bears well-developed sense orgAnswer:
(vi) Their body is covered externally by a chitinous exoskeleton.
(vii) Circulatory system is of open type.
(viii) Haemocoel present in them.
(ix) Male and female reproductive organs are separate.
Examples: Cockroach, crab, scorpion, bee, butterfly, mosquito, etc.

Question 17.
Write features of hemichordata phylum.
Answer:
Features of hemichordata are the following :
(i) They are worm-like unsegmented organisms.
(ii) They are all marine animals.
(iii) They may be solitary or colonial.
(iv) Their body is divisible into proboscis, collar, and trunk.
(v) They are bilaterally symmetrical.
(vi) Respiration takes place by gill slits.
(vii) Sexes are mostly separate.
Examples: Balanoglossus, Cephalodiscus, etc.

Question 18.
Write major differences of non-chordata and chordata.
Answer:
Non-chordata and chordata have following differences :
Non-Chordates:
1. There is no tail behind the anus.
2. Haemogloblin plasma dissolved in their blood.
3. Heart, if present, is dorsal.
4. Nervous system is ventral and solid.
5. Pharynx gill slits are absent

Chordates:
1. Tail is present behind their anus.
2. Haemoglobin is present in their red blood cells.
3. Heart is ventral and in a pericardial cavity.
4. Nervous system is dorsal and hollow.
5. Pharynx gill slits are present.

Question 19.
Write important features of chordata phylum and classified this phylum. Answer: Important features of chordata phylum are the following :
(i) Presence of nerve chord and hollow nervous system.
(ii) They all have paired gill slits.
(iii) Solid, elastic notochord occurs in all chordata and in any stage of life.
(iv) Presence of tail behind the anus stage.

Classification:
Chordata is divided into three subphyla:
(i) Urochordata
(ii) Cephalochordata
(iii) Vertebrata.

Essay Type Questions

Question 1.
Explain the classification of cryptogamae.
Answer:
Cryptogamae:
These are flowerless and seedless plants. They have hidden reproductive orgAnswer: They do not bear flowers and seeds externally.

They are divided into three divisions:

1. Thailophyta: They do not possess a stem, root or leaf and so called as thallus. Embryo formation after fertilization is absent. Their sex organs are single-celled. There is three clear group of plants in this division :
(A) Algae: Ulothrix, Cladophora, Ulva.
(B) Fungi: Aspergillus, Penicillium, Agaricus.
(C) Lichens: like Lichen perennail, Fruticose lichen.

2. Bryophyta:
The body of these plants are divided into structures like roots, stem or leaf. They grow on moist shady placed. Vascular tissue are absent in them. Their reproductive organs are multicellular. Embryo formation takes place after fertilisation.
Examples: Riccia, Funaria, Marchantia etc.

3. Pteridophyta:
The plant body is differentiated into root, stem and leaves. Vascular tissues are present in them. Their sex organs are multicellular. Embryo formation takes place after fertilization in them.
Examples: Fern (Pteris, selaginella).

Question 2.
Give the names of major phylurii with one or two features with examples.
Answer:
Major features with examples of the animal’s phylum are following:

Sub-Phylum	Phylum and its simple characters	Example
(i) Protozoa (unicellular)	1. Protozoa: They are single celled, their body shape is unlimited.	Amoeba, Euglena
(ii) Metazoa (multicellular)	2. Porifera: They are multicellular. Whole body in is perforated.	Sponges, Sycon
	3. Coelenterata: Stinging cells are present in them.	Hydra, Jellyfish, Obelia
	4. Platyhelminthes: The body of these worms are soft and flat. The true coelom absent in them.	Tapeworm, liverfluke
	5. Nematoda:They have cylindrical body made up of cutical. Alimentary canal is complete in them.	Ascaris (Hookworm)
	6. Annelida: They have long body with segments. True coelom present in them.	Earthworm, leech
	7. Arthropoda: They have segmented body. Respiration occurs by gill, tracheae, book lungs, etc.	Cockroach, Bee, Mosquito.
	8. Mollusca: Body is soft and covered with hard shell. Their body is unsegmented.	Pila, Octopus, Unio
	9. Echinodermata: Their body is covered with calcareous spines. They are unsegmented.	Sea-cucumber, Starfish.
	10. Protochordata: They possess a combination of invertebrate and choredata characters. Body is divided into proboscis, collar and trunk.	Balanoglossus Saccoglossus.
	11. Chordata: Nerve chord and gill slits occur in them. Presence of notochord in them.	Whale, Rat, Monkey

Practical Work

Experiment 1.
To differentiate between monocots and dicots.

Procedure:
Take some seeds of wheat, gram, pea, maize, rice, tamarind and put into water. When they swollen completely, then classified and note in table. Those have one cotyledon (wheat, maize, rice) are monocots and those have two cotyledons (gram, pea, tamarind) are dicots. Make table to see other difference in them.

Reason for difference	Monocot	Dicot
1. Root	Adventitious	Tap root
2. Leaf	Parallel veination	Reticulate veination
3. Stem	Noded	Without nodes
4. Seed	One cotyledon	Two cotyledons

Quick Review of the Chapter

1. Father of Taxonomy is:
(A) Aristotle
(B) Robert Hook
(C) De-Candoli
(D) Carolus Linnaeus
Answer:
(D) Carolus Linnaeus

2. Which is not the base for the classification of organisms like Monera?
(A) cell structure
(B) nutrition
(C) body organization
(D) habitat
Answer:
(D) habitat

3. Which animal is not Monera?
(A) diatom
(B) bacteria
(C) microplasma
(D) blue-green algae
Answer:
(A) diatom

4. Respiration in reptiles takes place:
(A) by gills
(B) by skin
(C) by lungs
(D) by skin and slits
Answer:
(C) by lungs

5. Mammalia animal is:
(A) seahorse
(B) chameleon
(C) ostrich
(D) whale
Answer:
(D) whale

6. Skeleton is hollow in:
(A) pisces
(B) amphibians
(C) reptiles
(D) aves
Answer:
(D) aves

7. Who does not contribute in the classification of animals in a large kingdom ?
(A) Ernst Haeckel
(B) Robert Whittaker
(C) Carl Woese
(D) Darwin
Answer:
(D) Darwin

8. Which scientist divided the Monera Kingdom into Archaebacteria and Eubacteria?
(A) Eichler
(B) Carl Woese
(C) Haeckel
(D) Carolus
Answer:
(B) Car! Woese

9. Which of the following is a gymnosperm plant?
(A) mango
(B) pea
(C) cycas
(D) guava
Answer:
(C) cycas

10. Which of the follow ing has outer covering?
(A) unio
(B) pila
(C) chiton
(D) all of the above
Answer:
(D) all of the above

11. Which of the following group have mammary glands?
(A) aves
(B) mammals
(C) reptiles
(D) none of the above
Answer:
(B) mammals

Haryana State Board HBSE 9th Class Science Important Questions Chapter 6 Tissues Important Questions and Answers.

Haryana Board 9th Class Science Important Questions Chapter 6 Tissues

Very Short-Answer Type Questions

Question 1.
Are there same types of tissues in plants and animals?
Answer:
No, plants and animals have different types of tissues.

Question 2.
How are newly cells formed?
Answer:
Through cell division process.

Question 3.
What is called as unicellular organisms?
Answer:
All those organisms in which all the biological activities are fulfilled through single cell are called as unicellular organisms.

Question 4.
Which organisms undergo labour division?
Answer:
Multicellular organisms.

Question 5.
How many types of tissues are there in plants?
Answer:
Two types:
(i) Meristematic tissues
(ii) Permanent tissues.

Question 6.
Where are Meristematic cells found?
Answer:
Dividing cells (meristematic tissues) found at the tip of the shoot and at the tip of the root.

Question 7.
What is the function of meristematic tissue?
Answer:
Building up of new cells.

Question 8.
Do the permanent tissues have the ability of divide?
Answer:
No.

Question 9.
How many types of permanent plant tissues are there?
Answer:
Two types:
(i) Simple tissues
(ii) Complex tissues.

Question 10.
What are Parenchymatous tissues ?
Answer:
Parenchymatous tissues can be living and oval, rounded elongated or polygonal in shape. They have thin cell wall and the cells are isodiametric.

Question 11.
What are collenchymatous tissues ?
Answer:
Due to deposition of cellulose and Pectin at the angles of these tissues they get thinken in size. These tissues do not have intercellular spaces.

Question 12.
What are sclerenchymatous tissues ?
Answer:
These are dead cells. These cells do not have any intercellular space in them. They provide strength to the plant parts.

Question 13.
What are simple permanent tissues ?
Answer:
These tissues are formed of parenchymatous cells. Their origin, structural formation and function are same.

Question 14.
Which part of the plant consists of meristematic tissues ?
Answer:
Green part of the plant.

Question 15.
What are protective tissues made up of?
Answer:
By sclerenchymatous tissues.

Question 16.
Which parts of the plant consists of protective tissues.
Answer:
Leaves, flowers, stem and roots.

Question 17.
What is the other name of sclereids ?
Answer:
Brachysclereids or stone cells.

Question 18.
What is called as complex tissue ?
Answer:
Cells of different shape and size together form a group which works out a special function, is called as complex tissue.

Question 19.
How many types of complex tissues are there ?
Answer:
Two type:
(i) Phloem
(ii) Xylem.

Question 20.
Name the tissue that transports food in plants. [H.B.S.E. March, 2019]
Answer:
Sieve elements (phloem).

Question 21.
How many types of animal tissues are there ? Write their names.
Answer:
Four types:
(i) Epithelial tissues
(ii) Connective tissues
(iii) Muscular tissues
(iv) Nervous tissues.

Question 22.
Where are epithelial tissues found ?
Answer:
In the external and internal layers of animals.

Question 23.
Which tissue is called a protective covering in animals ?
Answer:
Epithelial tissue.

Question 24.
Which tissue is responsible for producing sperm and egg in animals ?
Answer:
Epithelial tissue.

Question 25.
What are the types of muscular tissues ?
Answer:
Three types:
(i) striated
(ii) unstriated
(iii) cardiac muscles.

Question 26.
Which muscles function according to owr will ?
Answer:
Voluntary muscles (Striated muscles).

Question 27.
Which type of muscles present in heart ?
Answer:
Cardiac muscles.

Question 28.
How many types of connective tissues are there ?
Answer:
Three.

Question 29.
Write two main functions of connective tissues ?
Answer:
Joining different organs and provide protection.

Question 30.
What are the types of skeletal connective tissues ?
Answer:
Two types:
(i) Bone
(ii) Cartilage.

Question 31.
Which tissue functions to connect bone to another bone?
Answer:
Ligaments.

Question 32.
What do tendons interconnect with?
Answer:
Muscle with bone.

Question 33.
Write down the name of the fluid tissue found in the body.
Answer:
Blood.

Question 34.
How many types of blood cells or corpuscles are found in blood?
Answer:
Three types of blood cells or corpuscles.
They are:
(i) Erythrocytes-Red Blood Cells (RBC)
(ii) Leucocytes: White Blood Cells (WBC) and
(iii) Blood Platelets.

Question 35.
What is the fluid part in blood called as ?
Answer:
Plasma.

Question 36.
What percentage of water is there in blood ?
Answer:
90%

Question 37.
Which tissues are brain, spinal cord and nerves formed of ?
Answer:
Nervous tissues.

Question 38.
What is nervous tissue called as ?
Answer:
Neuron.

Question 39.
What is the main function of neuron ?
Answer:
Sending impulses of messages.

Short-Answer Type Questions

Question 1.
Multicellular organisms are more superior in comparison of unicellular organisms. Why ?
Answer:
The unicellular organism can accomplish but a few functions and in doing that they are comparatively less expert to that of multicellular organisms. Among multicellular organisms by forming groups of lacs of cells not only those functions, rather they can perform more functions with complete skill, since they have the quality of labour-division in them.

Question 2.
Is there some difference between plants and animals tissues ?
Answer:
The plant tissues perform the function of supporting. Most of the tissues of plants are dead. The dead tissues too provide mechanical strength like the living tissues. They need little care of maintenance, where as the animals roam about here and there in search of companion, food and shelter. They consume more energy than plants. They possess maximum number of living tissues. Growth in some parts of the plants remains constrained, whereas in animals the case is different.

Question 3.
What are the different types of tissues found in plants ?
Answer:
Two types of tissues are found in plants:
(1) Meristematic tissues
(2) Permanent tissues

Question 4.
Write down the features of meristematic tissues.
Answer:
The features of meristematic tissues are as follows :
(1) Meristematic cells have same structure and their cell wall is thin.
(2) The shape of the cells is round, oval or polygonal.
(3) They are compactly arranged with each other and they don’t have any intercellular space in them.
(4) These cells have dense or sufficient cytoplasm (cell liquid) and a big nucleus.
(5) They have comparatively few vacuoles or no vacuole.

Question 5.
Where are meristematic tissues found in plants ?
Answer:
Meristematic tissues are found in the growing up parts of the plants only; Like-apical meristem and cambium (the region that increases thickness)

Question 6.
Write down the characteristics of permanent tissues.
Answer:
The characteristics of permanent tissues are as follows:
(1) Permanent tissues are formed of meristematic tissues.
(2) Their cells have no ability of division.
(3) They have a definite shapes.
(4) Their wall can be dead, thin or thick.
(5) They have enlarged cells and vacuolic cytoplasm.

Question 7.
Differentiate between meristematic tissue and permanent tissue.
Answer:
The difference between meristematic tissue and permanent tissue is as follows:
Meristematic Tissue:
1. They do not have intercellular space.
2. They have the ability of divide.
3. The are responsible for growth.
4. They are thin-walled and isodiametric.
5. They have an enlarged nucleus.

Permanent Tissue:
1. It can be or cannot be there in them.
2. They lack the ability of division.
3. They are no responsible for growth.
4. They are thin or thick-walled but not isodiametric.
5. They have small nucleus.

Question 8.
What are permanent tissues?
Answer:
Permanent tissues:
Permanent tissues are formed of meristematic tissues. Their tissues have no ability of division. Their size and volume is definite.

Permanent tissues are of two types:
(1) Simple tissues
(2) Complex or compound tissues.

Question 9.
Differentiate between parenchyma and collenchyma tissues.
Answer:
Following are the differences between parenchyma and collenchyma:
Parenchyma Tissue:
1. They are found in roots, stem and leaves.
2. Their walls are not thick.
3. They are formed of round and fine walled cells.
4. Their wall is made up of pectin and cellulose.
5. They helps in storing food and provide mechanical support.
6. They have intercellular space in them.

Collenchyma Tissue:
1. They are found in the middle vein of the stem and leaves.
2. Their walls are thick.
3. They have thick and elongated wall.
4. Their cell wall possesses collens of pectin.
5. They just provide mechanical support.
6. It is absent in them.

Question 10.
Enunciate different types of simple permanent tissues and write down the function of each. Answer: Simple permanent tissues are of three types :
(a) Parenchyma
(b) Collenchyma
(c) Sclerenchyma

(a) Functions of Parenchyma:
(i) Storing of food and assimilation.
(ii) To provide mechanical strength to the parts of plant.
(iii) Storing of resin, tanin, gum particles, and resin of morganie waste material.
(iv) Due to presence of chloroplast or chlorenchyma, they prepare food themselves.

(b) Functions of Collenchyma:
(i) They provide flexibility and strength to the plants.
(ii) Due to presence of chloroplast or chlorenchyma, they prepare glucose and starch.

(c) Functions of Sclerenchyma:
(i) They provide more strength to cartex and hard seeds.
(ii) They get transformed into protective tissues and protect the interior parts.

Question 11.
Differentiate among parenchyma, collenchyma and sclerenehyma.
Answer:
Parenchyma:
1. Their cell wall is constructed ot pectin and cellulose.
2. These are living cells.
3. Their function is food-storage and providing support.
4. They are found in root, stem and leaves.
5. They are formed of rounded thin walled cells.

Collenchyma :
1. Their cell wall is also formed of pectin and cellulose.
2. They too have living cells.
3. Their function is to provide mechanical support.
4. They are found in the middle vein of leaf and stem.
5. They are formed of multiarmed cells.

Sclerenchyma:
1. Their cell wall is formed of lignin.
2. Their cells are dead.
3. Their function is only to provide support
4. They are found in the stem and pulp of the fruits.
5. They are formed of thick-walled cells.

Question 12.
Describe Sclerenchvmatous tissue.
Answer:
Sclerenchyma:
These ceils are elongated in size and thin but are equipped with lignin. These are dead cells and are attached together. These cells are pointed at both ends. There is a clear mid lamella between adjacent cells. Cells consist of skewed regions that are called as pit canals. The cells provide strength to the parts of the plant.

Question 13.
Name different components found in Xylem (xylem tissues) components.
Answer:
The four components found in Xylem (xylem tissues) are as follows:
(1) Tracheids,
(2) Vessels,
(3) Xylem or wood Parenchyma
(4) Wood or Xylem fibers.

Question 14.
Give the importance of phloem in plants.
Answer:
Importance of Phloem: It is planted conductive tissue. It transports the starch (food) prepared by leaves to different parts of the plant.

Question 15.
Write functions of the Xylem (xylem tissues).
Answer:
Functions of Xylem:
It is too plant conductive tissue. It’s function is to transport the absorbed water and dissolved mineral salts by the roots to the leaves of the
plants and the apex. It also provide mechanical power to the plant.

Question 16.
Write short note on protective tissue.
Answer:
Protective Tissue:
Sclerenchyma found in the outermost parts of plants gets transformed into protective tissues. These tissues remain in the external layer of leaves, stems and roots. These tissues protect the interior tissues of plants. These tissues are covered with cutin. The cells of cork are dead. Cork is a lighter and protective tissue, it is more compressible and does not catch fire quickly.

Question 17.
What is stomata? Write its functions.
Answer:
Stomata:
They are found in the epidermal cells of the lower surface of leaves of plants which are called as stomatal pore. Stomata get protected by two guard cells.

Functions:
(1) Stomata are the nostrils of plants.
(2) Stomata plays a vital role in the exchange of gases and through them water loss takes place in plants.

Question 18.
Write names of different tissues found in animals.
Answer:
Animal tissues:
There are four types of tissues found in animals.
(1) Epithelial tissue
(2) Connective tissue
(3) Muscular tissue
(4) Nervous tissue.

Question 19.
Give the names and important functions of animal tissues.
Answer:
Animal tissue:
(a) Epithelial tissues:
Functions: They participate in absorption, secretion, protection, excretion, etc.

(b) Connective tissue:
Functions: This tissue participates in interlink the various parts of the body, provide support, turgidity, storage, protection and transportation.

(c) Muscular tissue :
Functions: Muscular tissue participates in motion, conduction, contraction, etc.

(d) Nervous tissue:
Functions: These do the main work of controlling and management.

Question 20.
Write a typical note on epithelial tissue.
Answer:
This is a covering or outer protective tissue that cover the body of an animal. Also, it protects a number of organs and cavities inside the body. Skin, alimentary can be capillary tube’s coat, food pipe, hollow organs of lungs all are formed of epithelial tissues. There is very’ narrow space. In these tissues, the cells are compactly arranged.

Question 21.
Classify Epithelial tissues.
Answer:
On the basis of shape and functions of the cells, epithelial tissues are classified into following types:
1. Squamous epithelium: These flat and disc like cells help in covering the organs of the body providing protection to them.
2. Cubical epithelium: These cubical or isodiametric cells are found in ducts of salivary glands and kidney tubules.
3. Columnar epithelium: The pillar or column like wide cells found in the layer of stomach and intestine.
4. Ciliated epithelium: Columnar and cubical shaped ceils germinate hair like structures at their ends that are called as cilia.
5. Glandular epithelium: These cells are found in secretory glands.

Question 22.
Write down the functions of Epithelial tissue.
Answer:
The functions of Epithelial tissue are the following :
(1) It performs the function to protect and cover the body organs
(2) It performs the functions of secretion, (in the Stomach and salivary glands)
(3) It produces sensitivity. (Eye and retinal cells)
(4) It produces sperm and egg.
(5) These absorb water and other salts.
(6) They also play role in excretion.

Question 23.
Write down the functions of connective tissue.
Answer:
The functions of connective tissues are as follows :
(1) These tissues join different organs of body with one another.
(2) They perform the function to tieup up organs of the body.
(3) These tissues give support to the organs of the body.
(4) Bone and cartilage build up the skeleton of the body.
(5) Adipose tissues store fat.
(6) These tissue perform the function of blood circulation.
(7) White blood corpuscles (WBC) fight against harmful bacteria.

Question 24.
What is Blood?
Answer:
Blood:
Blood is a liquid connective tissue. It tissue drift in liquid plasma (matrix). Blood cells are callei
(i) Red blood corpuscles (RBC)-Erythrocytes
(ii) White blood corpuscles (WBC)-Leucocytes
(iii) Blood platelets
Blood runs in each part of the body and thus, it connects all the parts of the body.

Question 25.
What are the functions of blood ? Explain.
Answer:
Functions of Blood:
(1) Red blood corpuscles receive oxygen from lungs and send it to different parts of the body.
(2) Blood collects hormones from the hormone glands and sends it to different parts.
(3) It helps in excreting excretory products from the body.
(4) White blood corpuscles or leucocytes protects from harmful bacteria.
(5) Blood checks the body temperature.
(6) Blood platelets clots the blood and avoid the more discharge of blood out of the body.

Question 26.
What is Bone? What are its types ?
Answer:
Bone: Skeletal tissue is connective tissue. In this tissue, ’/3 part organic and 2/3 part inorganic material is found. Its matrix consists of a peculiar type of protein ‘ossein’ which is in the form of collagen fibres. Bone possesses matrix osteoblasts, cytus, fibers and matrix have calcium phosphate, calcium carbonate and calcium fluoride. It give strength to the bone.

Question 27.
What is compact bone ?
Answer:
Compact bone:
This bone used to be strong and hard. Inside the matrix of bone, calcium salts provide hardness to the bone. Compact bone is formed of round and irregular dense layers of bones. Compact bone is found in the long shaft of bones like-femur. It involves Haversian canals.

Question 28.
Write down two differences each between bone and cartilage.
Answer:
Following are the differences between bone and cartilage :
Bone Cartilage:
1. It’s matrix is hard and flexible.
2. It’s matrix is formed of condin.
3. It is covered with pericondrium.
4. Haversian system is absent in it.

bone:
1. It’s matrix is too rigid and strong.
2. It’s matrix is formed of ossein.
3. It is covered with peraosteium.
4. Haversian system is present in it.

Question 29.
Write down the difference between tendon and ligament. Answer: Following are the difference between tendon and ligament:
Tendon:
1. It is flexible and moulding.
2. It connects muscle with bone.
3. It is made up of yellow fibre.

Ligament:
1. it is inflexible and hard.
2. It connects bone with another bone.
3. It is made up of white fibred connective tissues.

Question 30.
Write down the functions of bone, cartilage tendon and ligament.
Answer:
(i) Bone : It constructs the structure of body and protects the soft orgAnswer:
(ii) Cartilage: It constructs the skeletons of cartilaginous fishes. In our body the tip of nose and external ear (pinna), is formed of it.
(iii) Tendon : It connects muscle with bone.
(iv) Ligament: It joins bone with another bone.

Question 31.
Write down the functions of skeletal tissue.
Answer:
Skeletal tissue: Skeletal tissue is rigid, there is sufficient quantity of calcium salts in bone-matrix. Following are the significant functions of skeletal tissue:
(1) Skeletal tissue enshapes the body.
(2) Skeletal tissue protect the sensitive organs of the body.
(3) Skeletal tissue helps in joining muscles together.
(4) This tissue provides movement and locomotion to the body.
(5) In the middle of the bones erythrocytes (RBC) are produced.
(6) It provides surface for attachment of muscles (tendons and ligaments).

Question 32.
What is areolar tissue?
Answer:
Areolar tissue:
This tissue is found below the skin, between the muscles, blood vessels and around the nervous tissue. These cells possess jelly types transparent and sticky matrix. This is connective tissue. It interlinks body cavity and other parts of the body.

Question 33.
What is muscular tissue ? What are its types ?
Answer:
Muscular tissue:
The cells of these tissues are elongated, spindle shaped and unbranched. Cardiac muscles are branched. Muscular tissues are found in different sizes. Muscular tissues provide locomotion and movement to different parts of body.

Muscular tissues are of three types :
(a) Striated muscles. (Skeletal or voluntary muscles)
(b) Unstriated muscles. (Smooth muscles or involuntary muscles)
(c) Cardiac muscles.

Question 34.
Make difference between striated muscles arid cardiac muscies.
Answer:
The differences between striated muscies and cardiac muscles are as follows:
Striated muscle:
1. These muscles work accordingly to our will i.e., they are voluntary muscles.
2. These muscles are jointed with bones.
3. They are unbranched.
4. They have a number of nuclei.
5. They have light or dark bands on them.

Cardiac muscle:
1. These muscles are involuntary, they do not work accordingly to our command.
2. These muscles are found in the heart.
3. They are branched.
4. They have one or two nuclei.
5. They have transverse indistinct light bands which show faint cross striations.

Question 35.
Describe the structure of skeletal and cardiac muscles.
Answer:
Skeletal Muscles:
We can move some muscles by the conscious will. Muscles present in our limbs move when we want them to, and stop when we so decide. Such muscles are called voluntary muscles. These muscles are also called skeletal muscles as they are mostly attached to bones and help in body movement. Under the microscope, these muscles show alternative light and dark bands or striations when stained appropriately. As a result, they are also called striated muscles. The cells of this tissue are long, cylindrical, unbranched and multinucleate (having many nuclei).

Cardiac Muscles: The muscles of the heart show rhythmic contraction and relaxation throughout life. These involuntary muscles are called cardiac muscles. Heart muscle cells are cylindrical, branched and uninucleate.

Essay Type Questions

Question 1.
What is called a tissue ? How many types of plant cells are there ? Describe meristematic tissues.
Answer:
Tissue:
A group of several cells that have common origin, structure and function is called a tissue. In plants there are two types of tissues.
(i) Meristematic tissues
(ii) Permanent tissues.

Meristematic Tissue:
In these tissues, division of cells takes places continuously and these cells that have the ability to divide, they keep on reproducing newly cells. Meristematic tissues are found only in those parts that participate in the growth process like tip of the shoot-root, and cambium. Due to these tissues, the length and thickness of the plants get increased.

On the basis of origination, meristematic tissues are of two types:
(i) Primary meristematic tissues.
(ii) Secondary meristematic tissues.

On the basis of position meristematic tissues are of three types:
(a) Apical meristem: They are found at the tip of the root, stem and branches; They are also of three types:
(1) Epidermis: These tissues buiid up the outer skin of the plant.
(2) Cortex: These tissues buiid up the filling up system.
(3) Hypodermis: These tissues make transport tissues, phioem and xylem,
(b) Intercalary meristem: This tissue is found in the stem of monocotyledones. Due to activity of this tissue plant grow up in height.
(c) Lateral meristem: This tissue is found in the stems and root of dicotyledones.

Question 2.
How many types of simple tissue of plant are there ? Explain them.
Answer:
Simple tissue When the meristematic tissues totally lose the ability of division, then they transform into permanent tissues. Permanent tissues are of two types: Simple tissues and complex tissues. Simple tissues are formed of only one type of same structural cells. Their function is also same. On the basis of structure these tissues are of three types:

(i) Parenchyma:
These tissues are found in the shoot system (stem, leaves and flower) and root in plants. In the green part of the plant their number used to be more. These cells can be round, elongated or polygonal shape. These are living cells. Their cell wall is thin and is made up of cellulose. These cells contain dense protoplasm. The main functions of these tissues are storage of food, assimilation, provide strength, storing of resin tanin and gum and many times preparing food too.

(ii) Collenchyma:
These cells too are living. These are multiarmed, oval and rounded shaped. Their cell wall is thin, but at the corners of the cell due to deposition of cellulose and pectin they get hard or stout. In these cells generally there are some chloroplasts. This tissue brings flexibility and strength in plants and prepare glucose and starch due to presence of chloroplast in it.

(iii) Sclerenchyma:
These cells are elongated in size and thin but are equipped with lignin. These are dead cells and are attached together. These cells are pointed at both ends. There is a clear mid lamella between adjacent ceils. Cells consist of askewed regions that are called as pit canals. The cells provide strength to the parts of plant.

Question 3.
What is called as complex tissues ? What are their types in plants ? Explain each of them.
Answer:
Complex Tissue:
Complex tissue is a group of more than one type of cells which perform a special function. Complex tissue is of two types :
(1) Xylem: Xylem is a transport tissue. It transports water and dissolved mineral salts from root to the shoot-system. All the cells of this tissue are dead, thick walled and lignified. This tissue is formed of with the combination of four cells.
(i) Trachieds
(ii) vessels
(iii) xylem or wood-parenchyma
(iv) xylem fibres.

(2) Phloem:
It is a living transport tissue. Starch prepared due to photosynthesis process is transported to different parts of the plant by it. This tissue is also formed of with the combination of four components :
(i) Sieve tubes
(ii) companion cells
(iii) phloem parenchyma
(iv) phloem fibres.
Out of these sieve tubes are significant. These sieve tubes consist of porous wall that send food from the leaves to different parts of the plant.

Question 4.
What is called as nervous tissue ? How many types does it have ?
Or
Define the neuron with diagram.
Answer:
Nerve cells (neurons): It is a specialised elongated cell which is the basic unit of conduction of impulses Tn this cell there a nucleus surrounded with cytoplasm. Many small branches project out of cytoplasm, which are called as dendrites. One of these branches is the longest one which is called as Axon. Axon carries the impulses away from cells. One nerve cell does not directly join with the another neuron. They have some empty space between them in which there is a very closed transportation. It is called as synapses.

If we have pain in our hand, this information gets collected by the dentrites of the sensory neuron located in the hand. The sensory neuron converts it into electric signal. This signal is transmitted by the motor neurons and passing through synapse reaches the brain. The brain on receiving the impulse reacts to that. The motor nerve carries this reaction to the muscles of the hand and thus, the muscles of the hand make suitable reaction.

Thus, nerve cells (neurons) are of three types:
1. Sensory nerve cells (neurons): They carry sensations in different parts of the body towards brain.
2. Motor neurons: These receive message from the brain and further send it to the muscles.
3. Multipolar neurons: They does both the functions they carry sensations towards brain and further carry the commands of brain towards the muscles.

Question 5.
What is blood (human blood) ? Explain its constituents.
Answer:
Blood: Blood is liquid connective tissue which is red in colour. Blood circulates in the organs of body, thus it can be said that it connects the entire parts of the body together.

Human blood has mainly two constituents:
(A) Plasma: This is a substance in the blood which is light yellow in colour. It contains 90% of water. The remaining salts, glucose, amino acid, protein, hormone, oxygen, carbon dioxide gas and certain digested undigested food materials are also found in it.

Function: It consists of fibrin named protein, that helps in coagulation or clotting of blood. It also consists anti bodies which destroy foreign bodies harmful bacteria etc.

(B) Blood corpuscles (Blood cells): There are three types of corpuscles found in blood which are described as ahead:

(a) Red Blood Corpuscles or Erythrocytes: These are round in shape. Each red corpuscle has the life time of nearly four months. They have a substance namely haemoglobin in them which provides red colour to blood. They are round in shape, flat and small in size. They have no nucleus in them. They have the largest number (50 lakh oer cubic milliletre).

Functions:
(i) Red blood corpuscles provide red colour to the blood.
(ii) Their haemoglobin distributes oxygen throughout the body. On receiving oxygen these corpuscles i become oxy-haemoglobin.

(b) White Blood corpuscles or Leucocytes : The number of white blood corpuscles is lesser than red blood corpuscles, but they are bigger in size than them. They are white in colour, since they have no haemoglobin in them. Therefore they do not have a definite shape. They also have nucleus. They are of five types.
Function: They kill the harmful bacteria in the body and gobble them up. Thus, they protect us from diseases.

(c) Thrombocytes or Platelets: They are thick in the centre and thin at the ends. They are very small. They also have nucleus.
Function: They help in coagulation of blood. When in case of injury, blood oozes out from the wound, these platelets gather around the injury and by a chemical action clot there, so that there might not be any more bleeding.

Practical Work

Experiment-1:
Observing the structure of stem by cutting it in a transverse section (T.S.).

Procedure:
(i) Peel off a thin slice or transverse section of a thin and soft stem of a plant, keep it into the safranine solution.
(ii) Take a slice of stem section and keep it on a glass slide carefully leave a drop of glycerine on it and cover it with a coverslip.
(iii) Observe the prepared slide under the compound microscope and draw a sketch diagram of the setting up of the cells that you observe.

Quick Review of the Chapter

1. Blood transports
(A) oxygen
(B) food
(C) harmones and waste substances
(D) all of the above
Answer:
(D) all of the above

2. Nearly all tissues of are dead.
(A) plants
(B) animals
(C) both (A) and (B)
(D) saprophytes
Answer:
(A) plants

3. New cells in plants are formed by tissues.
(A) parenchyma
(B) collenchyma
(C) meristematic
(D) sclerenchyma
Answer:
(C) meristematic

4. Which of the follow ing is not the characteristic of meristematic?
(A) highly active
(B) more cytoplasm
(C) vacuole present
(D) distinct nucleus
Answer:
(C) vacuole present

5 tissues are found in the growing up parts of root and stem.
(A) Parenchyma
(B) Meristematic
(C) Sclerenchyma
(D) Collenchyma
Answer:
(B) Meristematic

6. The helpful tissue in photosynthesis is :
(A) parenchyma
(B)
(C) sclerenchyma
(D)
Answer:
(A) parenchyma

7 tissues carries the function of storage.
(A) collenchyma
(B)
(C) sclerenchyma
(D)
Answer:
(B) parenchyma

8. The tissues which makes a plant hard and strong is :
(A) collenchyma
(C) parenchyma
Answer:
(B) sclerenchyma

9. Which tissues make up the husk of coconut ?
(A) sclerenchyma
(C) parenchyma
Answer:
(A) sclerenchyma

10. Sclerenchyma is found in the of a plant.
(A) stem
(B) near vascular bundle
(C) buds of leaves and seeds
(D) all of the above
Answer:
(D) all of the above

11. Holes/pores are found :
(A) on the surface of leaf
(B) in vessels
(C) in xylem
(D) in phloem
Answer:
(A) on the surface of leaf

12. Which of the following is not a function of epidermis ?
(A) reduces the loss of water
(B) protects from mechanical shocks against water cell
(C) helpful in entry of parasite fungi
(D) all of the above
Answer:
(C) helpful in entry of parasite fungi

13. The shape of protective cells/tissues in stomata is
(A) like liver
(B) like kidney
(C) like the seed of bean
(D) like the seed of gram
Answer:
(B) like kidney

14. The function of stomata is:
(A) evaporation
(B) intake and release of oxygen
(C) intake and release of carbon dioxide
(D) all of the above
Answer:
(D) all of the above

15. The capacity of water absorption in roots increases by:
(A) increase in the size of root
(B) increase in the length of root
(C) due to hair roots present on roots
(D) all of the above
Answer:
(C) due to hair roots present on roots

16. What makes bark impermeable for air and water ?
(A) waxy cover
(B) thick layer of bark
(C) chemical named subrin
(D) all of the above
Answer:
(C) chemical named subrin

17. The example of complex tissue is:
(A) xylem
(B) meristematic
(C) phloem
(D) both (A) and (C)
Answer:
(D) both (A) and (C)

18. ………….. is Conductive tissue.
(A) xylem
(B) phloem
(C) both (A) and (B)
(D) neither (A) nor (B)
Answer: (C) both (A) and (B)

19. The parts of xylem are:
(A) tracheids
(B) vessels
(C) xylem parenchyma and fibre
(D) all of the above
Answer:
(D) all of the above

20. The parts of phloem are:
(A) sieve tubes
(B) companion cells
(C) phloem parenchyma and fibres
(D) all of the above
Answer:
(D) all of the above

21. Minerals and water are transported by:
(A) phloem
(B) xylem
(C) sieve tube
(D) companion cells
Answer:
(B) xylem

22. Phloem conducts:
(A) synthesised food
(B) mineral salts
(C) water
(D) all of the above
Answer:
(A) synthesised food

23. Which tissue is not a simple tissue?
(A) sclerenchyma
(B) phloem
(C) parenchyma
(D) collenchyma
Answer:
(B) phloem

24. Which tissue is not an animal tissue?
(A) epithelial
(B) epidermal
(C) connective
(D) muscular
Answer:
(B) epidermal

25. Which tissue carries the function of covering the body and making covers for different organs inside the body?
(A) epithelium
(B) connective
(C) nervous
(D) muscular
Answer:
(A) epithelium

26. Which one is not a type of epithelium tissues?
(A) squamous
(B) cubical
(C) rounded
(D) columnar and ciliated
Answer:
(C) rounded

27. Which tissue forms the difference of alimentary canal and mouth?
(A) glandular
(B) squamous
(C) columnar
(D) cubical
Answer:
(B) squamous

28. What kind of tissue is blood?
(A) epithelium
(B) connective
(C) muscular
(D) nervous
Answer:
(B) connective

29. Which blood cells carries the function of intake of oxygen?
(A) RBC
(B) WBC
(C) platelets
(D) all of the above
Answer:
(A) RBC

30. Bone is an example of what type of tissue?
(A) epithelium
(B) connective
(C) muscular
(D) nervous
Answer:
(B) connective

31. The tissue which provides motion to body is:
(A) epithelium
(B) connective
(C) muscular
(D) all of the above
Answer:
(C) muscular

32. The feature of voluntary muscle is:
(A) long in size
(B) cylindrical
(C) unstriated
(D) all of the above
Answer:
(D) all of the above

33. Involuntary muscles are not found in:
(A) bones
(B) eyelids
(C) urinal
(D) trachea of lungs
Answer:
(A) bones

34. Which cell can be longest?
(A) epithelium
(B) nervous
(C) connective
(D) muscular
Answer:
(B) nervous

35. Which tissue rs found in heart?
(A) muscular
(B) nervous
(C) epithelium
(D) connective
Answer:
(A) muscular

Haryana State Board HBSE 9th Class Science Important Questions Chapter 5 The Fundamental Unit of Life Important Questions and Answers.

Haryana Board 9th Class Science Important Questions Chapter 5 The Fundamental Unit of Life

Very Short-Answer Type Questions

Question 1.
Who discovered the first cell and when?
Answer:
A scientist named Robert Hooke discovered the cell in 1665.

Question 2.
What was discovered by Leeuwenhoek?
Answer:
Leeuwenhoek discovered bacteria cells in 1674 with the help of a microscope.

Question 3.
Which scientist gave the name protoplasm to the living material inside the cell?
Answer:
J.E. Purkinje in 1939.

Question 4.
Which scientists proposed cell theory?
Answer:
M.Schleiden (1838) and T. Schwann (1839).

Question 5.
What is a cell ?
Answer:
The cell is the structural and functional unit of living organisms.

Question 6.
Which scientist expanded cell theory?
Answer:
Virchow (1855).

Question 7.
When was the electron microscope discovered?
Answer:
In 1940.

Question 8.
What is a unicellular organism?
Answer:
When a single cell of the organism performs all the life functions, it is called a unicellular organism.

Question 9.
What is a multicellular organism?
Answer:
When more than one cell group together to form an organism, it is called a multicellular organism.

Question 10.
Give some examples of unicellular organisms.
Answer:
Amoeba, Euglena, Entamoeba, Paramoecium.

Question 11.
Name one multicellular organism.
Answer:
Man.

Question 12.
Name the longest cell.
Answer:
Nerve cell.

Question 13.
Name the smallest cell.
Answer:
Mycoplasma galisepticum.

Question 14.
Which is the largest cell?
Answer:
Ostrich egg.

Question 15.
Name the smallest cell found in the human body.
Answer:
Lymphocyte.

Question 16.
Name the largest plant cell.
Answer:
Acetabularia.

Question 17.
Which cell organelle is responsible for protein synthesis?
Answer:
Ribosome.

Question 18.
In which organism is a division of labour found?
Answer:
In multicellular organisms.

Question 19.
What are cell organelles?
Answer:
In every cell, some specific components perform specific functions. They are called as cell organelles.

Question 20.
Cell organelles group together to form which unit?
Answer:
Cell.

Question 21.
Name the main functional zones oLa cell.
Answer:
The plasma membrane, nucleus cytoplasm.

Question 22.
Name one special feature of plasma membrane.
Answer:
Selective permeability.

Question 23.
What is osmosis?
Answer:
The movement of water or some other liquid substance from a region of high concentration to a region of low concentration through a semi-permeable membrane is called osmosis.

Question 24.
Give one example of osmosis.
Answer:
Absorption of water by plant roots.

Question 25.
Why does kishmish (dried raisin) get swollen in kheer?
Answer:
As the protoplasm of the kishmish is more concentrated than the kheer, internal osmosis takes place due to which it gets swollen.

Question 26.
What is diffusion?
Answer:
The movement of a substance from a region of high concentration to a medium of low concentration is called diffusion.

Question 27.
What happens when a cell is kept in a hypertonic solution?
Answer:
The cell will lose water by osmosis.

Question 28.
What is the membrane called which allows only specific substances to pass through it?
Answer:
Semi-permeable membrane.

Question 29.
What is plant cell wall made of?
Answer:
Cellulose.

Question 30.
Which cell organelle controls the activities of the cell?
Answer:
Nucleus.

Question 31.
Write the full form of RNA.
Answer:
Ribonucleic acid.

Question 32.
Write the full form of DNA.
Answer:
Deoxyribonucleic acid.

Question 33.
What is a gene?
Answer:
The functional unit of a chromosome is called a gene.

Question 34.
Which is the carrier of hereditary characters ?
Answer:
Chromosome.

Question 35.
How many chromosomes are found in man ?
Answer:
23 pairs or 46 chromosomes.

Question 36.
Name two cell organelles.
Answer:
Mitochondria, Golgi apparatus.

Question 37.
Which cell organelle is knows as suicide bag?
Answer:
Lysosome.

Question 38.
Name one secretive organelle of cell.
Answer:
Golgi apparatus.

Question 39.
Name the powerhouse of cell.
Answer:
Mitochondria.

Question 40.
What is ATP?
Answer:
ATP is the energy of the cell.

Question 41.
Name an organelle which is found only in plant tissue.
Answer:
Plastids.

Question 42.
Name the organelle which is helpful in cell division.
Answer:
Centrosome.

Question 43.
What are prokaryotic cells ?
Answer:
The cells which are small, have no cell organelle and have only one chromosome, are called prokaryotic cells.

Question 44.
What are eukaryotic cells ?
Answer:
Cells which are large in size, have cell organelle and more than one chromosome are called eukaryotic cells.

Question 45.
What is the green colour of plants due to ?
Answer:
Due to green pigment.

Question 46.
Name a prokaryotic cell.
Answer:
Bacteria.

Question 47.
Name a eukaryotic cell.
Answer:
Animal or plant cell.

Question 48.
What is cytoplasm ?
Answer:
The substance enclosed by the plasma membrane is called cytoplasm.

Question 49.
What is protoplasm ?
Answer:
Cytoplasm and nucleus together constitute protoplasm.

Question 50.
How many types of endoplasmic reticulum are there ?
Answer:
Two types:
(i) Rough Endoplasmic Reticulum (RER),
(ii) Smooth Endoplasmic Reticulum (SER).

Question 51.
What is the main function of SER ?
Answer:
To Synthesis lipid molecules.

Question 52.
What does ER denote ?
Answer:
Endoplasmic Reticulum.

Question 53.
Which organelle detoxifies toxic substances and drugs in the liver cells ?
Answer:
SER.

Question 54.
Name coloured plastids.
Answer:
Chromoplast.

Question 55.
Name a white and colourless plastid.
Answer:
Leucoplast.

Question 56.
Which plastid contains chlorophyll ?
Answer:
Chloroplast.

Question 57.
Are the vacuoles present in plants smaller or larger (in size)?
Answer:
Larger.

Short-Answer Type Questions

Question 1.
What is a cell ?
Answer:
Just as a house is made up of small bricks, living organisms are formed of small units called cells. Cell is the structural and functional unit of each living organism cell has its own organisation.

Question 2.
Write a note on the size of the cell.
Answer:
The size of the cell is so small that it is difficult to see it. It can be seen under a microscope, but to see and measure its structural organisation, a special unit called micron (p) on a micrometre is used. A micron is the l/000th part of a millimetre. Generally cells are around 30 microns in size. The smallest cell is mycoplasmas galisepticum and the largest cell is the egg of ostrich which is 170 x 135 mm in size. The size of pleuropneumonia is 0.1 pm. The size of the cell depends on the function it performs.

Question 3.
What is cell theory (principal) ?
Answer:
Cell is the basic unit of life. This is the cell theory. According to this theory, all living organisms are made up of cells. Cell is the functional and structural unit of life. Cell is a body containing protoplasm. Cell theory was proposed by M. Schleiden (1838) and T. Schwann (1839) after studying plant and animal cells. Afterwards, in 1855, Virchow expanded the cell theory by saying, ‘The new cells are formed from division of pre-existing cell.’ This is the cell theory.

Question 4.
What are unicellular and multicellular organisms ?
Answer:
1. Unicellular organisms:
The organisms which are formed of single cell are called unicellular organisms; e.g. amoeba, fungi, chlamydomonas, paramoecium, euglena etc.

2. Multicellular organisms:
The organisms which are formed of many cells grouped together are called multicellular organisms; e.g. hydra, whale, sponge, ferm, man, tagetus, fish, etc.

Question 5.
Draw a labelled diagram of the cells of onion peel as seen under a microscope.
Answer:
Cells of onion peel:

Question 6.
Draw a labelled diagram of various cells found in human body.
Answer:
Different cells of human body

Question 7.
What are the major differences between the cells of unicellular and multicellular organisms ?
Answer:
The main differences between the cells of unicellular and multicellular organisms are :
(1) The cell of a unicellular organism is generally circular or oval, while the cells of multicellular organisms are cylindrical.

(2) As a unicellular organism is made up of a single cell, all the life activities are performed by this single cell. On the other hand in multicellular organisms, all cells perform certain specific functions.

(3) As all the life activities are performed by a single cell in unicellular organisms, these activities are not performed efficiently. But division of labour is found in the cells multicellular organisms. Different cells perform specific functions, which they do efficiently.

(4) Amoeba, Paramoecium, etc. are unicellular organisms while dog, frog, man, etc. are multicellular organisms.

Question 8.
What are the advantages of multicellularity ?
Answer:
Multicellularity has a lot of advantages. Because of multicellularity, division of labour is found in higher animals. Because of difference in the types of cells, various cells perform specific functions in these organisms. All the cells co ordinate with each other. Thus, all the activities relating to growth and development depend upon the co ordination between all the cells.

Question 9.
What are the differences between plasma membrane and cell wall ? Give their functions also.
Answer:
Differentiate between Plasma Membrane and cell wall are as follows :
Plasma Membrane:
1. It is living.
2. It is formed of proteins, and lipid peptides.
3. It is smooth and flexible.
4. It is semi-permeable.

Cell Wall:
1. It is non-living.
2. It is formed of cellulose, lignin and pectin.
3. It is hard.
4. It is permeable.

Functions:
Plasma Membrane: Only molecules of definite size can pass through it. It is semi-permeable. It is a protective covering of the cell.

Cell Wall: It provides shape, size and protection to the cell.

Question 10.
What happens when we put an animal cell or a plant cell into a sugar solution ?
Answer:
The following can happen if we put a living cell in sugar solutions having different concentration:
(1) When put in a hypotonic solution, water will enter the cell by osmosis.
(2) When put in an isotonic solution,there will be no net movement of water through the cell membrane.
(3) When put in a hypertonic solution, the water will come out of the cell through osmosis.

Question 11.
How is diffusion important for a cell ?
Answer:
Diffusion plays an important role for the entry and exit of water and gases in and out of the cell. It helps the cell to get nutrition from the outside environment. The entry and exit of various molecules and in and out of the cell takes place by diffusion only.

Question 12.
What is cell wall ?
Answer:
Cell Wall: Cell wall is found only in plant cells. Some bacteria also possess cell wall. As the cell wall is made up of cellulose, it is permeable to water. Because of hardening of cellulose, it is non-living.

Question 13.
Write the advantages and disadvantages of cell wall.
Answer:

Advantages:
(1) It provides a definite shape to the cell.
(2) The cell remains structurally strong and protected.
(3) The plasma membrane remains protected.
(4) Because of its permeability, the cell wall maintains balance of different materials inside the cell.
(5) It prevents the cell from the attack of disease causing molecules.
(6) It provides a definite structure to the cell.

Disadvantages:
(1) The pace of cell division gets slowed down because of cell wall.
(2) It reduce the expanding power of cell.

Question 14.
Write a note on protoplasm shrinkage.
Answer:
If a plant cell is kept in a hypertonic solution, then exosmosis starts, i.e. water starts coming out of cytoplasm, due to which the cell wall loosens. If the hypertonic solution is highly concentrated, then the shrinkage of protoplasm continues. This process is called protoplasm shrinkage.

Question 15.
What are the main functional zones of a cell ?
Answer:
The main functional zones of a cell are plasma membrane, cysoplasm and nucleus which perform the following functions : ‘
1. Plasma membrane: It is the outer covering of every cell. It is made of lipids and proteins. It protects the cell and controls the movement of molecules inside and outside the cell.

2. Cytoplasm: Apart from the nucleus it constitutes the remaining part of the cell. It has various cell organelles like Golgibodies, mitochondria, endoplasmic, reticulum, ribosomes, lysosomes and cnloroplasts which perform various functions.

3. Nucleus: It is the main part of the cell, circular of oval-shaped. It controls all the activities of the cell. It contains nucleoplasm, nucleolus and chromosomes. Nucleus is covered by nuclear membrane.

Question 16.
Name the main cell organelles.
Answer:
The main cell organelles are:
(1) Endoplasmic Reticulum
(2) Ribosomes
(3) Lysosomes
(4) Mitochondria
(5) Nucleus
(6) Golgibodies
(7) Cilia and Plagella
(8) Vacuoles
(9) Plastids
(10) Centrosomes
(11) Perotisomes.

Question 17.
Write a note on nucleus.
Answer:
Nucleus is circular and the largest cell organelle found in the centre of cytoplasm. It controls and co ordinates all the activities of a cell. Nucleus is surrounded by nuclear membrane which is filled by nucleoplasm. Nucleolus and chromosomes are present in the nucleoplasm. There are some cells which possess many nuclei. These are called coenocytes.

Question 18.
Give four functions of nucleus.
Answer:
Functions of nucleus :
(1) It controls all the activities of the cell.
(2) It controls cell division.
(3) It takes part in reproduction.
(4) It maintains the functional ability of the cell.

Question 19.
Name both the nucleic acids present in the cell. What functions do they perform ?
Answer:
(1) DNA (Deoxyribose nucleic acid),
(2) RNA (Ribose nucleic acid).

(i) Functions of DNA: It contains genes. DNA stores the hereditary characters and passes these characters to the next generation. So, it is the hereditary material.
(ii) Functions of RNA: It synthesises proteins. In many types of viruses, RNA also acts as the hereditaiy material.

Question 20.
Write a note on Gene.
Answer:
Small granular structures present on the chromosomes are called genes. Genes are always found in pail’s on the chromosomes. One pair of genes controls one character. For example, our height is decided by a pair of two genes present in our body. Similarly, other characters/features of our body, like skin colour, colour of the eyes, etc. develop from a pair of genes each.

Question 21.
What are genes ? What is their function ?
Answer:
Gene:
Gene is a part of deoxyribonucleic acid (DNA). They are present on the chromosome, one above the other, in a specific order. Gene is the hereditary unit of life. In living organisms one character is controlled by one pair of genes. Genes hold the chloroplasts together.

Question 22.
Describe prokaryotic and eukaryotic cells.
Answer:
Prokaryotic and eukaryotic ceils are of following types:
1. Prokaryotic ceils: Pro means primitive (primary) and karyon means nucleus. These cells do not possess nuclear membrane. Only one chromosome is found in these ceils. The cell organelles are not enclosed by a membrane in these cells, like blue-green algae, bacterial cell.

2. Eukaryotic cells: Eu means continuous and karyon means nucleus. These cells have a well-defined nucleus which is enclosed by a nuclear membrane. More than one chromosomes are present in these cells, like plant and animal cells.

Question 23.
Define the following :
Protoplasm, cytoplasm, nucleoplasm.
Answer:
(i) Protoplasm : All the substances present inside the cell membrane constitute protoplasm. Protoplasm is the very basis of life. It performs all the activities of life.
It has two parts:
(a) Nucleus
(b) Cytoplasm.

(ii) Cytoplasm : Apart from the nucleus, the remaining part of the protoplasm is called cytoplasm. It contains living as well as non-living material. Many cell organelles are present in the cytoplasm i.e. Mitochondria, ribosomes, Golgibodies, lysosomes, vacuoler, endoplasmic reticulum etc.

(iii) Nucleoplasm : It is found inside the nucleus in which proteins, nucleolus, enzymes and chromosomes are present.

Question 24.
Write a note on Endoplasmic Reticulum (E.R.) Or White down the functions of Endoplasmic Reticulum (E.R.).
Answer:
Near the nucleus, a large network of membrane-bound tubes is found, which is called endoplasmic reticulum. These look like long tubules or round or oblong bags (vesicles). ER is of two types:
(i) Rough Endoplasmic Reticulum (RER),
(ii) Smooth Endoplasmic Reticulum (SER).
ER helps in intracellular transport of materials. It also acts as a cytoskeleton for some bio-chemical reactions. In the liver cells of vertebrates it plays a crucial role in detoxifying many poisons and drugs.

Question 25.
Differentiate RER and SER.
Answer:
Differences between RER and SER as below:
RER (Rough Endoplasmic Reticulum)
1. They are present on the surface of the ribosomes.
2. They, lie near the nucleus.
3. They help in photosynthesis.

SER (Smooth Endoplasmic Reticulum):
1. They don’t have any ribosomes.
2. They are present near the plasma membrane.
3. They help in lipid synthesis and in the formation of plasma membrane.

Question 26.
Write a note on Golgibodies.
Answer:
Golgibodies were first described by Camillo Golgi. The substance secreted by Golgibodies is accumulated in the vacuoles. Golgibodies form the cell wall. They are made up of vesicles, vacuoles and tubules. They are called golgi complex or golgi apparatus. It packages the materials produced by the ER and despatches it outside the cell.

Question 27.
Which cell organelle is called digestive bag and why ?
Answer:
Lysosome functions as a digestive bag in the cell.
Lysosomes occur in all the cells. These are spherical structures enclosed by a green coloured membrane. These contain many membrane bound small vesicles which are filled with catabolic substances lenzymes, also which are called as digestive bags which contain enzymes. These vesicles digest organic substances in the cell. These work as intercellular digestive system.

Lysosomes also function in digestion of food particles as well as worn-out cell organisms as a result of which old cells die. Therefore, they are also called ‘suicidal bags’ because during disturbances in cellular metabolism, when the cell gets damaged, lysosomes burst and the enzymes digest their own cell. RER make the digestive enzymes of the lysosomes.

Question 28.
Write a note on lysosomes.
Answer:
Lysosomes: Lysosomes are sac like structures which are also called as suicidal bags. They are found in all cells. In each cells, there are over one hundred lysosomes. They were discovered by D. Dueve, a scientist, in 1955. Their function is the elimination of some disturbances in the cell as well as destruction of foreign particles. Many digestive enzymes are found in them due to which they are also called digestive enzymes.

Question 29.
What is a centrosome ?
Answer:
Centrosome: Centrosome is a spherical structure found near the nucleus. It is found only in animal cells and is totally absent in plant cells. It contains one or two centrioles. In plant cells, polar caps are present instead of centrosomes. Centrosome play an important role in cell division.

Question 30.
Write a note on ribosomes.
Answer:
They are made up of RNA and proteins. These extremely small bodies are either scattered freely in the cytoplasm or are attached on the outer surface membrane of the rough endoplasmic reticulum. In the cell, ribosomes systhesise proteins with the help of amino acids.

Question 31.
Write a note on mitochondria.
Answer:
Mitochondria is a spherical or rod-shaped important organelle of the cell bounded by two membranes. The outer membrane is smooth but the inner layer contains folds. These folds are called cristae. In between the two membranes, a fluid called matrix is present. Mitochondria produces respiratory enzymes. It also oxidises food to produce energy, so it is also called as energy house or power house of the cell.

Question 32.
Differentiate the structural organisation of lysosomes and mitochondria.
Answer:
Differences between the structural organisation of lysosomes and mitochondria are as follows :
Lysosomes:
1. These are sac like structures
2. These are enclosed by a single membrane.
3. They do not bear any folds on the inner surface.
4. They contain digestive enzymes, which digest the food material.
5. They do not contain DNA.

Mitochondria:
1. These are spherical or rod-shaped organelles.
2. These are enclosed by a double membrane.
3. They bear folds on the inner surface, which are called cristae.
4. They contain some specific enzymes, which help in respiration.
5. They contain DNA.

Question 33.
Give differences between the functions of lysosomes and mitochondria.
Answer:
Differences between the functions of lysosomes and mitochondria as follows :
Lysosomes
1. They produce energy by digesting stored food in the times of emergency.
2. They do not contain ATP.
3. The destroy viruses and bacteria.
4. They function to destroy old and damaged cell organelles.
5. Through destructive process, they destroy the unwanted materials and are also called as suicidal bags.

Mitochondria
1. They produce energy through respiration.
2. They store energy in ATP and release it according to the requirement.
3. They do not do so.
4. They are not capable to perform such functions.
5. They do not perform any protective functions.

Question 34.
Write any five differences between ribosomes and centrosomes.
Answer:
Differences between ribosomes and centrosomes are as follows:
Ribosomes:
1. These are granular and spherical structure.
2. These are found both in plant and animal cells.
3. They synthesise proteins from the amino acids.
4. They do not take part in cell division.
5. They are found either scattered freely in the cytoplasm or attached to the Rough Endoplasmic Reticulum.

Centrosomes:
1. These are small star-like structure present outside the nuclear Wall.
2. These are found only in the animal cells.
3. They do not take part in protein synthesise.
4. They form Aster Rays at the time of cell division.
5. They occur in pairs near the nucleus.

Question 35.
Write a brief note on chloroplasts.
Answer:
Chloroplast is found in all green-coloured plants. It a double membrane cell organelle on the inner membrane of which are found flat structures, thylakoids, the number of which is innumerable in a chloroplast. Thylakoids are held together in a granum. Chloroplast plays an important role in photosynthesis. Green coloured pigment called chlorophyll found in chloroplast. Its ground matter is called stroma.

Question 36.
Write a note on plastids.
Answer:
Plastids are present only in plant cells. They are of two types:
(1) Chromoplast (coloured plastid).
(2) Leucoplast (white and colourless plastid).
The plastid having green pigment is called chloroplast. It is essential for photosynthesis. Yellow and purple coloured pigments are also found in chloroplasts. Plastids also contain their own DNA and ribosomes.

Question 37.
Why does papaya look yellow, spinach look green and watermelon look red from inside ?
Answer:
Different pigments present in plants impart different colours in them. The pigment named carotene gives yellow colour to papaya, green pigment chlorophyll in spinach gives it green colour; xanthomycin pigment gives red colour to the inside of the watermelon. So, different colours found in plants are due to different pigments.

Question 38.
Write a note on vacuoles.
Answer:
Vacuoles are the storage sacs for solid or liquid materials. Vacuoles are small in size in animal cells whereas plant cells have larger vacuoles. In plant cell, vacuoles provide turgidity and rigidity to the cells. They play an important role in the disposal of waste products from the body.

Essay Type Questions

Question 1.
Explain the microscopic structure of an animal cell.
Answer:
Microscopic structure of an animal cell: The basic unit of life in living organism is called a cell. It is a small sized structure filled with protoplasm. The body of every animals is formed by grouping together of many cells. The shape ofthe cell varies and their number also varies (from organism to organism). Cell has two main parts:
(a) Cell membrane,
(b) Protoplasm.

(a) Cell membrane:
A cell is enclosed by a thin membrane which is made up of plasma. It is very thin, soft and smooth. Cell membrane is semi-permeable. It gives shape to the cell and protects the protoplasm in it. It controls the movement of material inside and outside the cell.

(b) Protoplasm:
All the material present inside the cell membrane constitutes protoplasm. In fact, protoplasm is the basis of life. All life activities are completed in the protoplasm. Protoplasm has two main parts:
(1) Nucleus,
(2) Cytoplasm.

1. Nucleus:
Every cell has a spherical structure in its centre known as nucleus. Nucleus controls all the activities of the cell. Nucleus has four main parts nuclear membrane, nucleoplasm, chromatin reticulum, nucleolus. Nucleus is enclosed by a double membrane which is attached to endoplasmic reticulum. Nucleus contains DNA, RNA and substance chromatin which is made up of proteins. Chromosomes are found on the thread-like structures which constitute chromatin. Chromosomes are composed of DNA and protein. Chromosomes carry the hereditary traits from parents to offspring through genes. In the centre of the nucleus is present a dense, dark straining organelle called nucleolus. It stores RNA in it and helps in cell division.

2. Cytoplasm: Protoplasmic material of the cell other than nucleus is called cytoplasm. It contains living as well as non-living particles.

Following cell organelles are present in the cytoplasm:

(i) Mitochondria: These are double membraned spherical or rod-shaped structures. Mitochondria contains DNA, RNA and respirator)’ enzymes. These are helpful in respiration. Mitochondria are also called energy houses or powerhouses of the cell.

(ii) Ribosomes: These are spherical structures composed of RNA and protein. They are found scattered freely throughout the cell cytoplasm in prokaryots. However, in eukaryotic cells they are found either in free state in the cytoplasm or attached on the outer surface membrane of RER.

(iii) Endoplasmic Reticulum:
It is a large network of membrane-bound tubules. ER communicates both with plasma-membrane as well as nuclear membrane. Ribosomes are found on its outer surface membrane (in case of RER). It is a network formed of proteins and lipids. It helps in the transport of materials within the cell. It establishes contact between cytoplasm and nucleus.

(iv) Golgibodies:
These are membrane-bound structures found near the nucleus. Its function is not so clear or distint, but it helps in the formation of cell wall and despatches the material synthesised in ER outside the cell.

(v) Centrosome:
It is a small spherical structure found near the nucleus. It contains one or two granules, the centrioles. It helps in cell division.

(vi) Lysosomes:
These are spherical or oval structures present inside the cell. They contain digestive enzymes. Lysosomes help in digestive activity and destruction of damaged cell organelles.

(vii) Vacuoles:
These are a few spherical or egg shaped regions in the cell where there is very little cytoplasm. These are called vacuoles. Vacuoles help in the disposal of poisonous material from the cell as well as in the storage of food particles. In some unicellular organisms, specialised vacuoles also help in expelling excess water outside the cell.

(viii) Cilia and Flagella:
These are some thin, hair-like structures which help in movement of the organism in a fluid medium. Cilia are more in number but smaller in size whereas flagella are one or two in number. Their length is comparatively more.

Question 2.
What is a nucleus ? Write its functions.
Answer:
Every cell has a nucleus present in the centre. It is spherical or oval-shaped. The cell which have more than one nucleus is called coenocyte.

Following are the main parts of a nucleus :
1. Nuclear membrane: It is a thin and elastic membrane which keeps the nucleus separate from the cytoplasm.
2. Nucleoplasm: The fluid present inside the nucleus is called nucleoplasm.
3. Nucleolus: It is present inside the nucleus and controls the synthesis of protein.
4. Chromosomes: Every nucleus contains thin and long structures called chromosomes. Chromosomes are composed of a substance called nucleoprotein. This substance is formed by the joining of nucleic acids and proteins. The number of chromosomes for one type‘of organisms is fixed.

Functions of Nucleus: Following are the functions of a nucleus:
(i) The main function of the nucleus is to control and coordinate the activities of the cell.
(ii) A cell cannot remain alive without a nucleus.
(iii) It controls the hereditary characters with the help of genes.

Question 3.
What are the main functions of:
(a) Plasma membrane
(b) Mitochondria
(c) Chromosomes
(d) Nucleolus
(e) Lysosomes
(f) Cell wall
(g) Ribosome
(h) Golgi apparatus
(j) Peroxisomes ?
Answer:
The main functions of each cell constituent are as follows :
(a) Plasma membrane: Being semi-permeable, it controls the movement of materials inside and outside the cell.
(b) Mitochondria: It is the powerhouse of the cell. It oxidises carbohydrates to produce energy.
(c) Chromosomes: They are the carriers of hereditary traits and DNA is present in them.
(d) Nucleolus: It synthesises ribosomes.
(e) Lysosomes: It functions as a digestive sac,/bag because it plays the role of intercellular digestion.
(f) Cell wall: It protects the internal contents of the cell.
(g) Ribosomes: These help in protein synthesis.
(h) Chloroplast: Its green pigment produces food during photosynthesis.
(i) Golgi apparatus: It forms lysosomes and peroxisomes.
(j) Peroxisomes: They are helpful in the oxidation reactions.

Practical Work

Experiment 1:
To observe osmosis with dried raisin.

Procedure:
(1) Take 3-4 dried raisins and put them in water. After 30 minutes observe them. Raisins swell because water enters them by osmosis.
(2) Place the swollen raisins in concentrated sugar solution and observe after half an hour. Raisins shrink because water in them moves to the solution because of osmosis.

Experiment 2:
To prepare a temporary slide of onion peel.

Procedure:
(1) Take onion peel from its concave side and place it in the watch glass containing water.
(2) Put a drop of water on a glass slide and with the help of a brush transfer the onion peel from the watch glass to the slide (on the drop of water) and put a drop of iodine and place a cover slip on it. Take care that there is no air bubble beneath the coverslip.
(3) Observe this under a compound microscope and make a diagram of the cells as per your observation.

Quick Review of the Chapter

1. Who coined the term ‘cell’?
(A) Robert Brown
(B) Robert Hooke
(C) M. Schielden
(D) Virchow
Answer:
(B) Robert Hooke

2. Which substance ¡s used by Robert Hooke in discovery of cell?
(A) membrane of an onion
(B) cork
(C) a leaf
(D) Toot of a plant
Answer:
(B) cork

3. Which scientist discovered living cells first of all?
(A) Robert Hooke
(B) Leeuwenhoek
(C) Virchow
(D) Robert Brown
Answer:
(B) Leeuwenhoek

4. Who discovered the nucleus of a cell?
(A) Purkinje
(B) Virchow
(C) Robert Brown
(D) Robert Hooke
Answer:
(C) Robert Brown

5. Who gave the name protoplasm to the living material inside the cell?
(A) Purkinje
(B) Robert Brown
(C) M. Schleiden
(D) Virchow
Answer:
(A) Purkinje

6. Who proposed ‘Cell Theory’?
(A) M. Schleiden
(B) T. Schwann
(C) Virchow
(D) both (A) and (B)
Answer:
(D) both (A) and (B)

7. …………… is not a unicellular organism.
(A) Amoeba
(B) Euglena
(C) Ferns
(D) Paramoecium
Answer:
(C) Ferns

8. When was electron microscope discovered?
(A) in 1936
(B) in 1940
(C) in 1942
(D) in 1944
Ans.
(B) in 1940

9. Which organelle is not found in all organisms?
(A) plasma membrane
(B) cell wall
(C) nucleus
(D) cytoplasm
Answer:
(B) cell wall

10. Which organelle allows in and out of materials and stops them?
(A) plasma membrane
(B) cytoplasm
(C) nuclei’s
(D) centrosome
Answer:
(A) plasma membrane

11. The process of osmosis is related to:
(A) plasma membrane
(B) cell wall
(C) selective permeable membrane
(D) nucleus membrane
Answer:
(C) selective permeable membrane

12. The use of osmosis process ¡s carried out in the plants as:
(A) absorption of water by roots
(B) exchange of gases in leaves
(C) intake of nutrition from outside environment
(D) all of the above
Answer:
(D) all of the above

13. Which is not a feature of plasma membrane?
(A) flexible
(B) formed of lipid, protein
(C) study possible under simple microscope
(D) absence of selective permeable feature
Answer:
(D) absence of selective permeable feature

14. Plant cell wall is composed of which substance?
(A) minerals
(B) fats
(C) cellulose
(D) glucose
Answer:
(C) cellulose

15. The longest cell of human body is:
(A) RBC
(B) WBC
(C) neuron cell
(D) skin cell
Answer:
(C) neuron cell

16. Which is non-living?
(A) plasma membrane
(B) cell wall
(C) golgibodies
(D) ribosome
Answer:
(B) cell wall

17. Which waste require to be excreted out by the cell?
(A) CO₂
(B) O
(C) water
(D) all of the above
Answer:
(A) CO₂

18. controls all functions of a cell.
(A) centrosome
(B) golgi apparatus
(C) nucleus
(D) chromosome
Answer:
(C) nucleus

19. Where are chromosomes found?
(A) in nucleus
(B) in nucleolus
(C) in protoplasm
(D) in cytoplasm
Answer:
(A) in nucleus

20. Hereditary characters are found in
(A) nucleus
(B) chromosome
(C) nucleolus
(D) mitochondria
Answer:
(B) chromosome

21. Which substance forms chromosome?
(A) DNA
(B) Protein
(C) fat
(D) both (A) and (B)
Answer:
(D) both (A) and (B)

22. The functional unit of a chromosome is called
(A) chioroplast
(B) chromosome
(C) gene
(D) lamella
Answer:
(C) gene

23. The feature of prokaryotic is not:
(A) small size
(B) nucleus present
(C) only one chromosome
(D) nucleus is not surrounded by nucleus membrane
Answer:
(B) nucleus present

24. The feature of eukaryotic ¡s not:
(A) small size
(B) nucleus region fully developed
(C) nucleus is found
(D) more than one chromosome
Answer:
(A) smaLl size

25. Ribosomes synthesise ………..
(A) fats
(B) proteins
(C) carbohydrates
(D) all three
Answer:
(B) proteins

26. What is formed by endoplasmic reticulum (ER)?
(A) respiratory system
(B) food synthesis system
(C) reticulum system
(D) all three
Answer:
(C) reticulum system

27. Which organelle detoxifies toxic substances and drugs in the liver cells?
(A) ER
(B) goigi apparatus
(C) lysosome
(D) vacuoles
Answer:
(A) ER

28. Which scientist told about Golgi apparatus first of all?
(A) Virchow
(B) Purkinje
(C) Camino
(D) T. Schwann
Answer:
(C) Camillo

29. Lysosome is formed by
(A) ER
(B) golgi apparatus
(C) vacuole
(D) mitochondria
Answer:
(B) Golgi apparatus

30. Which is not an organ of an animal cell? ‘
(A) plasma membrane
(B) cytoplasm
(C) vacuole
(D) cell wall
Answer:
(D) cell wall

31. How many m are there in ijtm?
(A) 106
(B)
(C) l0
(D) 106
Answer:
(A) l06

32. What is the name of system of disposal of waste of a cell?
(A) golgi apparatus
(B) vacuoles
(C) lysosome
(D) centrioles
Answer:
(C) lysosome

33. ………. is called a suicidal bag.
(A) golgi apparatus
(B) lysosome
(C) ER
(D) plastid
Answer:
(B) lysosome

34. ………….. is called powerhouse of a cell.
(A) centriole
(B) Golgi bodies
(C) mitochondria
(D) plastid
Answer:
(C) mitochondria

35. plays an important role in photosynthesis.
(A) m mitochondria
(B) ch chloroplast
(C) vacuole
(D) Golgi bodies
Answer:
(B) chloroplast

36. pigments are found in the chloroplast.
(A) green
(B) yellow
(C) pink
(D) all above mentioned
Answer:
(A) green

37. are storage sacs of solid or liquid substances.
(A) lysosome
(B) golgi apparatus
(C) vacuoles
(D) ER
Answer:
(C) vacuoles

38. In which ‚ear cell was discovered?
(A) 1565
(8) 1605
(C) 1600
(D) 1665
Answer:
(D) 1665

39. The fundamental organizational unit of life is:
(A) Chromoplasts
(B) Cell
(C) Leucoplasts
(D) Plasma
Answer:
(B) Cell

Haryana State Board HBSE 9th Class Science Important Questions Chapter 4 Structure of the Atom Important Questions and Answers.

Haryana Board 9th Class Science Important Questions Chapter 4 Structure of the Atom

Very Short-Answer Type Questions

Question 1.
How are materials formed?
Answer:
Materials are formed with the combination of atoms and molecules.

Question 2.
What is known as Atom?
Answer:
Atom is the microscopic indivisible particles that have an independent existence.

Question 3.
During which century did Dalton agree an atom to be indivisible?
Answer:
During 19th century, Dalton agreed an atom to be indivisible.

Question 4.
Which are the basic particles of an atom ?
Answer:
The basic particles of an atom are electrons, protons and neutrons.

Question 5.
Define isobars with examples.
Answer:
Atoms of different elements which have same mass number but different atomic numbers are known as isobars. For example, calcium (₂₀Ca⁴⁰) and argon (₁₈Ar⁴⁰) are isobars.

Question 6.
What is meant by electron ?
Answer:
In an atom, the negatively charged particle whose mass is \(\frac {1}{2000}\) part mass of a proton that revolves around the nucleus is called an electron.

Question 7.
Which scientist gets the honor of discovering electron?
Answer:
J.J. Thomson.

Question 8.
Which charge does remain on an electron?
Answer:
Negative (-ve) charge.

Question 9.
Which scientist discovered the canal Rays?
Answer:
The German scientist, E. Goldstein.

Question 10.
Which other name is called as the canal rays ?
Answer:
Canal rays are also called as positive rays.

Question 11.
Which electron are canal rays attracted towards in the electronic field ?
Answer:
Towards negative electron.

Question 12.
How are electron and proton represented ?
Answer:
Electron is represented by e~ and proton is represented by p+.

Question 13.
What is the mass and charge of proton ?
Answer:
The mass of proton is 1 unit and the charge is +1.

Question 14.
How much is the charge on an electron ?
Answer:
An electron has -1 charge.

Question 15.
Why is atom electrically neutral ?
Answer:
Because in an atom the number of electrons and protons mutually balance the charges.

Question 16.
Which discovery enabled J.J. Thomson to win the Nobel Prize in Physics ?
Answer:
For discovery of‘electron’.

Question 17.
When was J.J. Thomson born ?
Answer:
J.J. Thomson was born on 18 December, 1856.

Question 18.
What is the mass of‘alpha’ particles ?
Answer:
The mass of ‘alpha’ particles is 4u.

Question 19.
What are alpha particles?
Answer:
Alpha particles are binary-charged helium particles.

Question 20.
Which scientist is known as the father of nuclear physics?
Answer:
E. Rutherford is called as the father of nuclear physics.

Question 21.
When was E. Rutherford born?
Answer:
E. Rutherford was born on 30 August 1871.

Question 22.
According to Rutherford, where does the entire mass of an atom lie in ?
Answer:
In the micronucleus of the atom.

Question 23.
Compare the size of the nucleus with respect to that of the size of an atom.
Answer:
The size of the nucleus is 1O3 times less than that of the size of an atom.

Question 24.
Which charge does atom-nucleus have?
Answer:
Positive charge.

Question 25.
Of which element’s nucleus is known as proton?
Answer:
Of hydrogen nucleus.

Question 26.
What was the proposal of Neils Bohr regarding the revolving of electrons?
Answer:
According to Neils Bohr electrons revolve in a certain energy orbit.

Question 27.
According to Neils Bohr model, when an electron returns from a higher level orbit to a lower level orbit, then the difference of energy gets radiated into which form?
Answer:
Electromagnetic radiation or in the form of light.

Question 28.
Which particles does the nucleus of an atom have?
Answer:
Protons and Neutrons.

Question 29.
How many a maximum number of electrons can be accommodated in the first and second orbit of an atom?
Answer:
In the first orbit, two and in the second orbit, maximum of eight electrons can be accommodated.

Question 30.
Write down the name of the lightest atom.
Answer:
Hydrogen.

Question 31.
Write down the name of that atom which does not have any neutron.
Answer:
Protium (₁¹H ) which is an isotope of hydrogen.

Question 32.
Write down the number of proton and neutron present in the nucleus of helium.
Answer:
There are two protons and two neutrons in the nucleus of helium.

Question 33.
When and who discovered the neutron ?
Answer:
Chadwick discovered neutron in 1932.

Question 34.
In the structure of atom the electrons of which orbit determine the properties of atoms.
Answer:
The electrons in the last shell (valence shell).

Question 35.
In a single molecule of water, how many atoms of hydrogen and oxygen are there?
Answer:
In a single molecule of water, there are two atoms of hydrogen and one atom of oxygen.

Question 36.
Which atoms are chemically active?
Answer:
The atoms whose outermost shells are not complete are chemically active.

Question 37.
Which atoms are chemically neutral?
Answer:
Those atoms whose outermost shells are complete are chemically neutral. For example; helium and neon.

Question 38.
Give names of two bivalent atoms.
Answer:
(i) Calcium (Ca)
(ii) Berkelium (Be).

Question 39.
What is the valency of chlorine?
Answer:
One.

Question 40.
What will be the number of neutrons in the atom of the element whose atomic number is 19 and mass number is 39?
Answer:
Neutron = mass number – atomic number = 39 – 19 = 20

Question 41.
Why is the mass of the atom M and its ion M+ same?
Answer:
Because both have same number of neutrons and protons.

Question 42.
Write dow n two isotopes of uranium.
Answer:
²³⁵₉₂U and ²³⁸₉₂U

Question 43.
Which two of the following nuclei are isotopes mutually?
₉₀Z²³¹, ₉₁Z²³⁰, ₈₈Z²³⁰, ₉₀Z²³³
Answer:
₉₀Z²³¹ and ₉₀Z²³³

Question 44.
How many isotopes does carbon have ?
Answer:
Carbon has two isotopes 12 C and 14 C .

Question 45.
What are the atoms called that belong to only one element, which has same atomic number but different mass number?
Answer:
Isotopes.

Question 46.
What is the average mass of isotopes of chlorine?
Answer:
The average mass of isotopes of chlorine used to be 35.5u.

Question 47.
Which of the followings are nuclear isotopes?
₈₈Z²²⁶, ₈₇Z²³⁶,₈₈Z²³⁸,₈₈Z²³⁸
Answer:
₈₈Z²²⁶, ₈₈Z²³⁸,

Question 48.
Which radioactive isotope is used in the treatment of cancer ?
Answer:
Isotope of cobalt of mass number 60.

Question 49.
Which fuel is used in a nuclear plant ?
Answer:
In a nuclear plant, isotope of uranium (U-235) is used as fuel.

Question 50.
Which elements isotopes are used in treatment of goitre disease ?
Answer:
Isotopes of iodine are used in the treatment of goitre disease.

Question 51.
Write down names of two isobaric elements.
Answer:
Calcium and argon are isobaric elements.

Short-Answer Type Questions

Question 1.
Why are canal rays called as positive charged rays ?
Answer:
Falling of the canal rays towards negative electrons in the electric field shows that these rays are jointly made up of positively charged particles.

Question 2.
Write down the properties of canal rays.
Answer:
Following are the properties of canal rays:
(1) These rays move in a straight line.
(2) These rays are bent towards negative electrode in electric and magnetic field.
(3) They have mass many times more than the mass of electron.

Question 3.
Why are electrons called as planetary electrons in an atom ?
Answer:
In an atom, electrons revolve in their respective fixed large elliptical orbits just like planets in the sky revolve around the sun in their large elliptical orbits. Hence, electrons are called as planetary electrons.

Question 4.
Enunciate similarities and dissimilarities between protons and neutrons.
Answer:
Similarities between protons and neutrons:
(1) Mass of proton and neutron is approximately equal to a single atomic mass unit.
(2) Proton and neutron both exist in the nucleus of an atom.

Dissimilarities between protons and neutrons:
(1) Protons are positively charged particles, whereas neutrons are neutral particles.
(2) The mass of a neutron is somewhat more than that of the mass of a proton.

Question 5.
Write down the difference between electron and neutron.
Answer:
Following is the difference between electron and neutron.

Electron:
1. Electron possesses negative (-ve) charge.
2. They revolve around in different orbits outside the nucleus.
3. Their mass is the 1/2000th part by mass of a hydrogen atom.

Neutron:
1. Neutron possesses negligible charge.
2. They remain inside the nucleus.
3. Their mass is almost the same to that of the mass of an atom of hydrogen.

Question 6.
Write down the difference between electron and proton.
Answer:
Following is the difference between electron and proton :
Electron:
1. They possess unit (-ve) charge on them.
2. Their mass is l/’2000th part mass of an atom of hydrogen.
3. They revolve around in their respective orbits outside the nucleus.

Proton:
1. They possess unit (+ve) charge on them.
2. Their mass is almost the same to that of the mass of an atom of hydrogen.
3. They remain in the nucleus.

Question 7.
Explain the essential properties of the atomic nucleus.
Answer:
The essential properties of the atomic nucleus are as follows:
(1) The size of the atomic nucleus is 105 times smaller than the size of the atom itself i.e., its size is 10^-5A or 10^-15 m.
(2) Atomic nucleus is positively charged.
(3) Absolute mass of the atom remains to withstand into the nucleus.
(4) Most of the space around the atomic nucleus remains unoccupied.

Question 8.
Compare the properties of atomic nuclei and electron.
Answer:
The comparison of properties of atomic nucleus and electron is as follows:

Atomic Nucleus:
1. It possesses +ve charge on it.
2. It is situated in the central part.
3. Its mass is almost equal to that of the mass of the atom.

Electron:
1. It possesses (-ve) charge on it.
2. It revolves around the nucleus.
3. Its mass is l/2000th part mass of hydrogen atom.

Question 9.
What are the fundamental contributions of E. Rutherford to understand the structure of atom ?
Answer:
To understand the structure of atom, E. Rutherford gave a model of atom, according to which electrons were assumed revolving around the nucleus in their pre-planned orbits, it was just like as the planets in our solar system revolve around the sun in their fixed orbits. Besides, he told that the absolute mass of atom lies in its 4vely charged nucleus which is of the size 10^-15 m .

Question 10.
Is the number of electrons in different shells of an atom constant or inconstant ? Illustrate with examples.
Answer:
The number of electrons in different shells of an atom is constant. The distribution of electrons in different shells is done on the basis of Quantum Equation i.e., 2n²; where n indicates the serial number of the orbit like:

Quantum	Orbit	Maximum electron
1	K	2 x 12 = 2
0	L	2 x 22 = 8
3	M	2 x 32 = 18
4	N	2 x 42 = 32

This distribution of electrons was conceived by Bohr and Bury. According to them, the valence shell (outermost shell) cannot accommodate more than eight electrons and second last shell cannot accommodate more than 18 electrons.

Example:
Hydrogen has only single orbit where only 1 electron is there. 2 electrons of helium revolve in the first orbit. Lithium has 3 electrons out of which the third electron enters the second shell. Similarly in the atom of calcium there are 20 electrons out of which in the first shell there are 2, in the second and third orbit 8-8 and in the fourth shell there are 2 electrons.

Question 11.
Define valency. How is it related to atomic structure?
Answer:
Valency:
Valency of an atom is the number of valence electrons, whereas valence electrons are the electrons of the valence shell of any atom. The valency of an element and the valency of the electrons present in its outermost shell have the following relationship :
(1) The elements that have 1-4 electrons in their valence shells, their valency is equal to that of the electrons present in the valence shell.

(2) The elements that have 5-8 electrons in their valence shells, their valency is equal to the (8-electrons existing) outermost shell of the element.

(3) In the valence shell of helium, due to two electrons, its outermost shell gets filled up completely, that is why the valency of helium is zero. Similarly, the valency of other active gases is zero because the outermost shells get accommodated.

Normally, valency of metals = number of electrons present in the outermost shell and valency of non-metals = 8- number of electrons present in the outermost shell. Therefore, we can say that valency is related to the atomic structure, since the valency of electrons present in the valence shell is known only by atomic structure.

Question 12.
What are valence electrons? How many valence electrons are there in Mg and Al ?
Answer:
Valence electrons present in the outermost orbit are known as valence electrons.
The atomic serial number of Mg and A1 is 12 and 13 respectively. Their electronic configuration is:
Mg – 2,8,2
Al – 2,8,3
Therefore, we come to know that the number of valence electrons in Mg and Al is 2 and 3 respectively.

Question 13.
Describe the distribution of electrons in different orbits of the following atoms : lithium, nitrogen, neon, magnesium and silicon.
Answer:

Element	Atomic number	Distribution of Electrons in different shells
N			K	L	M
Lithium (Li)	3	2	1
Nitrogen (N)	7	2	5
Neon (Ne)	10	2	8
Magnesium (Mg)	12	2	8	2
Silicon (Si)	14	2	8	4

Question 14.
In the given hint ₂₀⁴⁰Ca , write down the mass number of calcium, atomic number, electronic configuration and atomic structure.
Answer:
Mass number = 40
Atomic number = 20
Electronic configuration = 2, 8, 8,2

Structure of nucleus :
Number of protons = 20
Number of neutrons = 40 – 20 = 20

Question 15.
How many of the following are protons and neutrons ?
¹⁴N₇ ¹⁴C₆ ¹⁵P₁₅
Answer:
(1) ¹⁴N₇
Atomic mass = 14
Atomic number = 7
Number of protons = 7
Number of neutrons = Atomic mass – atomic number = 14 – 7 = 7

(2) ¹⁴C₆
Atomic mass = 14
Atomic number = 6
Number of protons = 6
Number of neutrons = Atomic mass – atomic number
= 14 – 6 = 8

(3) ¹⁵P₁₅
Atomic mass = 31
Atomic number = 15
Number of protons = 15
Number of neutrons = Atomic mass – atomic number
= 31 – 15 = 16

Question 16.
Explain the chemical neutrality and chemical reactivity of atom.
Answer:
The chemical properties of an atom depend upon the schematic system of setting up of electrons in it. When the valence shell of an atom of an element gets filled up completely, then that element does not participate in chemical reaction, that is, such an atom is chemically neutral, for example neon, argon, etc. When the outermost shell of an atom of any element is not completely filled up, then such an atom is chemically reactive. The law of chemical reactivity depends upon the distribution system of electrons.

Question 17.
Why are inert or inactive gases behaviourally inactive?
Answer:
The valence shell in inert gases remains filled up completely. In helium, being the first orbit it gets completed due to two electrons. In rest of the inert gases it gets filled up with 8 electrons. Thereby, the electronic configuration of inert gases used to be stable. The cause of neutrality of these elements is the difficulty of entrance or exit of the electrons. It needs more energy to out electrons out of them more on so they also do not have the efficiency of acquiring electrons.

Question 18.
Boron has two isotopes ₅B¹⁰ (19%) and ₅B¹¹ (81%). Find average atomic weight for Boron.
Answer:
Average atomic mass of Boron atom = [10 x \(\frac {19}{100}\) + 11 x \(\frac {81}{100}\) ]
= \(\left[\frac{190}{100}+\frac{891}{100}\right]\) = [1.90 + 8.91] = 10.81 = 11

Essay Type Questions

Question 1.
Who discovered the nucleus of atom and how ?
Answer:
The nucleus of atom was discovered by Ernest Rutherford by experimenting with the scattering of alpha particles.

In this experiment, Rutherford happened to bombard a high speed stream of alpha particles on a thin foil of gold and he found that after striking the gold leaf, the alpha particles generally deflect from their path by an angle of 1°. One of the smallest parts of the alpha particles get scattered by a larger angular deflecting and come back after getting deflected very little.

It is a general fact that alpha particles are too much energetic particles. Their deflection of forming of bigger angle shows that they had hit against the total mass of atom of the substance. On the basis of this demonstration, he concluded that:

(i) The central part of the atom i. e., the nucleus is solid and has positive charge. The nucleus possesses approximately the total mass of the atom.
(ii) This central part of atom has a very’ small size as compared to the atom itself.

Question 2.
What new concept was introduced in Neils Bohr model of an atom by him ?
Answer:
Neils Bohr proposed a model of atom in 1912 A.D., which was basically based upon the new concept. These concepts are:

(1) Electrons revolve around the nucleus in fixed orbits and each orbit has a different radius.
(2) Each orbit does have its definite energy. Accordingly, the orbit located near the nucleus possesses the least energy and the orbit situated farthest from the nucleus possesses the maximum energy.
(3) When an electron moves to the orbit of a lower energy level from the higher energy level, then the difference of energy is emitted in the form of electromagnetic radiation or in the form of light.
(4) All around the nucleus to fill up the different orbits or shells the number of electrons does have a definite number.
(5) Electrons can constantly revolve in a stable orbit in the form of electromagnetic waves without radiating energy.
(6) If energy is propagated to the electron with a definite energy level, it can enter the orbit with a higher energy level.

Question 3.
What are the similarities in the electronic configuration of the following atoms?
(i) Lithium, Sodium, Potassium
(ii) Helium, Neon, Argon
(iii) Beryllium, Magnesium and Calcium.
Answer:
(i) Lithium, Sodium, Potassium:

Element	Atomic Number	Electron Distribution
		K	L	M	N
Lithium	3	2	1
Sodium	11	2	8	1
Potassium	19	2	8	8	1

In the above electron distribution, we learn that there is only one or single electron in the valence shell of all the three atoms of the elements i.e. Lithium, Sodium and Potassium due to that reason the valency of all these elements is the same.

(ii) Helium, Neon, and Argon:

Element	Atomic Number	Electron Distribution
		K	L	M	N
Helium	2	2
Neon	10	2	8
Argon	18	2	-8	8

From the above electron distribution, it is learned that the valence shells (outermost shells) of the atoms of all the three elements i.e., Helium, Neon and Argon are completely filled up, due to that reason their valency is zero or all these elements are inert or inactive.

(iii) Beryllium, Magnesium and Calcium:

Element	Atomic Number	Electron Distribution
		K	L	M	N
Beryllium	4	2	2
Magnesium	12	2	8	2
Calcium	20	2	8	8	2

From the above electron distribution we learn that in the atoms of all three elements, there are two electrons in the valence shell. Because of that reason, all the valency of all these elements is 2.

Question 4.
Explain with suitable examples the experimental uses of radioactive isotopes.
Answer:
Following are the experimental uses of radioactive isotopes :
(1) It can help in fixing the age of the earth, rocks, hills, meteors, etc.
(2) It can be used to find the thickness of paper, glass, plastic, etc.
(3) It can be used in finding out the cracks and crevices in the pipes.
(4) It helps in knowing the wear and tear in the machines.
(5) Isotopes are used in the treatment of different diseases in the medical field; e.g., CO-60 for curing cancer; isotope of iodine for curing thyroid, isotope of phosphorus for leukemia (blood cancer), etc.
(6) The radiations emitted through the radioactive isotopes are used in the form of high disease resistance in growing crops like wheat, paddy and groundnut (peanut).
(7) Isotopes are used in reforming fertilizers.
(8) Isotope Fe-59 is used to examine anemia

Question 5.
Show the electronic distribution of the first 20 elements in the Periodic Table.
Answer:
The electronic distribution of the first 20 elements in the periodic table is:

Atom	Hint	Number of Electrons	Arrangement of electrons in orbits	Distribution of electrons	Valency
Hydrogen	H	1	1 in the first orbit	1	1
Helium	He	2	2 in the first orbit	2	2
Lithium	Li	3	2 in the first orbit + 1 in the second orbit	2, 1	1
Berylium	Be	4	2 in the first orbit + 2 in the second orbit	2,2	2
Boron	B	5	2 in the first orbit + 3 in the second orbit	2, 3	3
Carbon	C	6	2 in the first orbit + 4 in the second orbit	2,4	4
Nitrogen	N	7	2 in the first orbit + 5 in the second orbit	2,5	3
Oxygen	0	8	2 in the first orbit + 6 in the second orbit	2, 6	2
Fluorine	F	9	2 in the first orbit + 7 in the second orbit	2,7	1
Neon	Ne	10	2 in the first orbit + 8 in the second orbit	2,8	0
Sodium	Na	11	2 in the first orbit + 8 in the second orbit+ 1 in the third orbit	2, 8, 1	1
Magnesium	Mg	12	2 in the first orbit + 8 in the second orbit + 2 in the third orbit	2, 8,2	2, 8,3
Aluminium	Al	13	2 in the first orbit + 8 in the second orbit + 3 in the third orbit	2, 8,3	2, 8,4
Silicon	Si	14	2 in the first orbit + 8 in the second orbit + 4 in the third orbit	2, 8,4	2,8,5
Phosphorus	P	15	2 in the first orbit + 8 in the second orbit + 5 in the third orbit	2,8,5	2, 8,6
Sulphur	s	16	2 in the first orbit + 8 in the second orbit + 6 in the third orbit	2, 8,6	2, 8,7
Chlorine	Cl	17	2 in the first orbit + 8 in the second orbit + 7 in the third orbit	2, 8,7	2, 8, 8
Argon	Ar	18	2 in the first orbit + 8 in the second orbit + 8 in the third orbit	2, 8, 8	2, 8, 8, 1
Potassium	K	19	2 in the first orbit + 8 in the second orbit+ 8 in the third orbit + 1 in the fourth orbit	2, 8, 8, 1	2, 8, 8, 2
Calcium	Ca	20	2 in the first orbit + 8 in the second orbit + 8 in the third orbit + 2 in the fourth orbit	2, 8, 8, 2	2, 8,3

Practical Work

Experiment 1:
Prove experimentally that when two bodies are rubbed against each other, charge is produced.

Procedure:
(1) Take a comb and rub it against the dry hair. Bring the comb near to the paper-bits. We notice the comb attracts the paper-bits to it. This proves that on rubbing two bodies against each other, a charge gets produced.

(2) Rub a glass rod with a silken cloth on bringing this glass rod near to the balloon, the balloon will get attracted to the charged glass rod. Thus, the experiment proves that on rubbing the glass rod against the silken cloth, the glass rod gets charged.

Experiment 2:
Explain with an experiment Rutherford’s scattering of alpha (a) particles.

Procedure:
To understand Rutherford’s scattering alpha (a ) particles experiment is performed in the open ground. Suppose a child is standing in front of a wall with their eyes shut. Now, ask him to throw some stones against the wall from at a short distance. On striking every stone against the wall, he will hear a sound.

If he repeats the activity ten times, he will hear the sound ten times. But if the child with his eyes shut throws the stones against a wall surrounded with barbed wire, most of the stones will not strike against that boundary and hence, no sound will be heard. As there is enough blank space in between the boundary, through which the stone escapes.

Quick Review of the Chapter

1. Which scientist discovered Canal Rays ?
(A) Dalton
(B) Li. Thomson
(C) E. Goldstein
(D) Neils Bohr
Answer:
(C) E. Goldstein

2. Which scientist discovered electrons ?
(A) Thomson
(B) Dalton
(C) Goldstein
(D) Neils Bohr
Answer:
(A) Thomson

3. When was J.J. Thomson awarded Nobel Prize ?
(A) in 1878
(B) in 1902
(C) in 1906
(D) in 1912
Answer:
(C) in 1906

4. Which scientist proposed that an atom consists of positively charged sphere and the electrons are embedded in it ?
(A) Rutherford
(B) Thomson
(C) Dalton
(D) Neils Bohr
Answer:
(B) Thomson

5. E. Rutherford discovered
(A) atom
(B) nucleus
(C) proton
(D) neutron
Answer:
(B) nucleus

6. The radius of nucleus is times than the radius of an atom.
(A) 105
(B) 104
(C) 103
(D) 102
Answer:
(A) 105

7. Which scientist told that when electrons revolve in discrete orbits, then energy ?
(A) Neils Bohr
(B) Rutherford
(C) Dalton
(D) Thomson
Answer:
(A) Neils Bohr

8. Who is the author of the book ‘Atomic Theory’ ?
(A) Rutherford
(B) Thomson
(C) Neils Bohr
(D) both (A) and (B)
Answer:
(C) Neils Bohr

9. Charge on nucleus of an atom is:
(A) zero charge
(B) negative charge
(C) positive charge
(D) no charge
Answer:
(C) positive charge

10. When was neutron discovered?
(A) in 1902
(B) in 1912
(C) in 1922
(D) in 1932
Answer:
(D) in 1932

11. Who discovered neutron?
(A) J. Chadwick
(B) J ,J. Thomson
(C) Neil Bohr
(D) None of the above
Answer:
(A) J. Chadwick

12. The characteristic of electron is not:
(A) uncharged
(B) mass same as proton
(C) found in nucleus
(D) it has negative charge
Answer:
(D) it has negative charge

13. The characteristic of electron is not:
(A) positively charged
(B) represents by e-
(C) negatively charged
(D) lightest particle
Answer:
(A) positively charged

14. The characteristic of proton is not:
(A) found in nucleus
(B) represents by p+
(C) mass 1 unit
(D) negatively charged
Answer:
(D) negatively charged

15. The first electron shell of an atom can have maximum electrons.
(A) 2
(B) 8
(C) 18
(D) 32
Answer:
(A) 2

16. The maximum number of electrons in third electron shell can be:
(A) 8
(B) 12
(C) 18
(D) 32
Answer:
(C) 18

17. The number of electrons in fourth electron shell can be:
(A) 8
(B) 18
(C) 32
(D) 2
Answer:
(C) 32

18. What will be the atomic number of an element having 6 electrons in its M shell?
(A) 8
(B) 16
(C) 24
(D) 34
Answer:
(B) 16

19. The number of electrons present in outermost shell of neon:
(A) 2
(B) 8
(C) 18
(D) 32
Answer:
(B) 8

20. Which of the following element is inert gas?
(A) neoft
(B) argon
(C) cripton
(D) all of the above
Answer:
(D) all of the above

21. The number of electrons present in the outermost shell of fluorine
(A) 2
(B) 5
(C) 7
(D) 17
Answer:
(C) 7

22. The number of electrons in electrons in outermost shell can be:
(A) 2
(B) 8
(C) 18
(D) 32
Answer:
(B) 8

23. What is the number of neutrons in hydrogen
(A) zero
(B) one
(C) two
(D) four
Answer:
(A) zero

24. Protium is an isotope of which element ?
(A) helium
(B) hydrogen
(C) lithium
(D) nitrogen
Answer:
(B) hydrogen

25. The symbol of tritium is:
(A) ₁¹H
(B) ₁²H
(C) ₁³H
(D) ₁⁴H
Answer:
(C) ₁³H

26. Deuterium is an isotope of which element?
(A) uranium
(B) lithium
(C) helium
(D) hydrogen
Answer:
(D) hydrogen

27. …………. is used as fuel in atomic furnace.
(A) Lithium
(B) Helium
(C) Uranium
(D) Beryllium
Answer:
(C) Uranium

28. The isotope of which element is used in the treatment of cancer ?
(A) Cobalt
(B) Iodine
(C) Boron
(D) Chlorine
Answer:
(A) Cobalt

29. the isotope of iodine is used in the treatment of ……………. disease
(A) atomic nucleus
(B) electron
(C) proton
(D) neutron
Answer:
(A) atomic nucleus

30. If K and L shell of an atom are full, then the number of electrons in it will be:
(A) 16
(B) 8
(C) 17
(D) 18
Answer:
(D) 18

31. For Which invection is Rutherfords alpha scattering experement responsible?
(A) atomic nucleus
(B) electron
(C) proton
(D) neutron
Answer:
(A) atomic nucleus

32. The number of electrons in Cl^– ion is:
(A) 16
(B) 8
(C) 17
(D) 18
Answer:
(D) 18

33. Which is correct electronic configuration of sodium ?
(A) 2, 8
(B) 8, 2, 1
(C) 2,8,1
(D) 8,2
Answer:
(C) 2, 8, 1

34. The fundamental particle of an atom is not:
(A) electron
(B) positron
(C) proton
(D) neutron
Answer:
(B) positron

35. Which one of the following is a correct electronic configuration of chlorine?
(A) 2, 7, 8
(B) 2, 8, 7
(C) 7, 8, 2
(D) 1, 8, 8
Answer:
(B) 2, 8, 7