# Selina solutions for Concise Physics Class 9 ICSE chapter 3 - Laws of Motion [Latest edition]

## Chapter 3: Laws of Motion

Exercise 3 (A)Exercise 3 (B)Exercise 2 (B)Exercise 3 (C)Exercise 3 (D)Exercise 3 (E)
Exercise 3 (A) [Pages 59 - 60]

### Selina solutions for Concise Physics Class 9 ICSE Chapter 3 Laws of Motion Exercise 3 (A) [Pages 59 - 60]

Exercise 3 (A) | Q 1.1 | Page 59

Explain giving two examples of following :
Contact forces

Exercise 3 (A) | Q 1.2 | Page 59

Explain giving two examples of following :
Non - contact forces

Exercise 3 (A) | Q 2 | Page 59

Classify the following amongst contact and non - contact forces:

Frictional force

Normal reaction force

Force of tension in a string

Gravitational force

Electrostatic force

Magnetic force

Exercise 3 (A) | Q 3 | Page 59

Give one example in each case where :

The force is of contact, and

Force is at a distance

Exercise 3 (A) | Q 4.1 | Page 59

A ball is hanging by string from the ceiling of the roof. Draw a neat labelled diagram showing the forces acting on the ball and the string.

Exercise 3 (A) | Q 4.2 | Page 59

A spring is compressed against a rigid wall. Draw a neat and labeled diagram showing the forces acting on the spring.

Exercise 3 (A) | Q 4.3 | Page 59

A wooden block is placed on a table top. Name the forces acting on the block and draw a neat and labelled diagram to show the point of application and direction of these forces.

Exercise 3 (A) | Q 5 | Page 59

State one factor on which the magnitude of a non-contact force depends. How does it depend on the factor stated by you?

Exercise 3 (A) | Q 6 | Page 60

The separation between two masses is reduced to half. How is the magnitude of gravitational force between them affected?

Exercise 3 (A) | Q 7 | Page 60

State the effects of a force applied on

1. A non-rigid, and
2. A rigid body.

How does the effect of the force differ in the two cases?

Exercise 3 (A) | Q 8 | Page 60

Give one example in each of the following cases where a force:

(i) Stops a moving body.
(ii) Moves a stationary body.
(iii) Changes the size of a body.
(iv) Changes the shape of a body.

Exercise 3 (A) [Page 60]

### Selina solutions for Concise Physics Class 9 ICSE Chapter 3 Laws of Motion Exercise 3 (A) [Page 60]

Exercise 3 (A) | Q 1 | Page 60

Which of the following is a contact force:

• Electrostatic force

• Gravitational force

• Frictional force

• Magnetic force

Exercise 3 (A) | Q 2 | Page 60

The non - contact force is :

• Force of reaction

• Force due to gravity

• Tension in string

• Force of friction

Exercise 3 (B), Exercise 2 (B) [Page 63]

### Selina solutions for Concise Physics Class 9 ICSE Chapter 3 Laws of Motion Exercise 3 (B), Exercise 2 (B) [Page 63]

Exercise 3 (B) | Q 1 | Page 63

Name the physical quantity that causes motion in a body.

Exercise 3 (B) | Q 2 | Page 63

Is force needed to keep a moving body in motion?

Exercise 3 (B) | Q 3 | Page 63

A ball moving on a table top eventually stops. Explain the reason .

Exercise 3 (B) | Q 4 | Page 63

A ball is moving on a perfectly smooth horizontal surface. If no force is applied on it, then will its speed decrease, increase or remain unchanged?

Exercise 3 (B) | Q 5 | Page 63

What is Galileo's law of inertia?

Exercise 3 (B) | Q 6 | Page 63

State Newton's first law of motion.

Exercise 3 (B) | Q 7 | Page 63

State and explain the law of inertia (or Newton's first law of motion).

Exercise 3 (B) | Q 8 | Page 63

What is meant by the term inertia?

Exercise 3 (B) | Q 9 | Page 63

Give qualitative definition of force on the basic of Newton's first law of motion.

Exercise 3 (B) | Q 10 | Page 63

Name the factor on which the inertia of a body depends and state how does it depend on the factor stated by you .

Exercise 3 (B) | Q 11 | Page 63

Give two examples to show that greater the mass, greater is the inertia of the body.

Exercise 3 (B) | Q 12 | Page 63

'More the mass, the more difficult it is to move the body from rest'. Explain this statement by giving an example.

Exercise 3 (B) | Q 13 | Page 63

Name the two kinds of inertia.

Exercise 3 (B) | Q 14 | Page 63

Give one example of each of the following :
(a) inertia of rest, and (b) inertia of motion .

Exercise 3 (B) | Q 15 | Page 63

Two equal and opposite forces act on a stationary body. Will the body move? Give a reason to your answer.

Exercise 3 (B) | Q 16 | Page 63

Two equal and opposite forces act on a moving object. How is its motion affected? Give reason.

Exercise 3 (B) | Q 17 | Page 63

An aeroplane is moving uniformly at a constant height under the action of two forces (i) Upward force (lift) and (ii) Downward force (weight). What is the net force on the aeroplane?

Exercise 3 (B) | Q 18 | Page 63

Why does a person fall when he jumps out from a moving train ?

Exercise 3 (B) | Q 19 | Page 63

Why does a coin, placed on a card, drop into the tumbler when the card is rapidly flicked with a finger?

Exercise 3 (B) | Q 20 | Page 63

Why does a ball thrown vertically upwards in a moving train , come back to the thrower's hand ?

Exercise 3 (B) | Q 21.1 | Page 63

Explain the following :
When a train suddenly moves forward , the passenger standing in the compartment tends to fall backwards .

Exercise 3 (B) | Q 21.2 | Page 63

Explain the following :
When a corridor  train suddenly starts , the sliding doors of some compartments may open .

Exercise 3 (B) | Q 21.3 | Page 63

Explain the following :
People aften shake branches of a tree for getting down its fruits .

Exercise 3 (B) | Q 21.4 | Page 63

Explain the following :
After alighting from a moving bus , one has to run for some distance in the direction of bus in order to avoid falling .

Exercise 3 (B) | Q 21.5 | Page 63

Explain the following :
Dust particles are removed from a carpet by beaitng it .

Exercise 2 (B) | Q 21.6 | Page 63

Explain the following :
It is advantageous to run before taking a long jump .

Exercise 3 (B) [Page 64]

### Selina solutions for Concise Physics Class 9 ICSE Chapter 3 Laws of Motion Exercise 3 (B) [Page 64]

Exercise 3 (B) | Q 1 | Page 64

The property of inertia is more in :

• a car

• a truck

• a horse cart

• a toy car

Exercise 3 (B) | Q 2 | Page 64

A tennis ball and a cricket ball , both are stationary. To start motion in them .

• a less force is required for the cricket ball than for the tennis ball .

• a less force is required for the tennis ball than for the cricket ball

• same force is required for both the balls .

• nothing can be said .

Exercise 3 (B) | Q 3 | Page 64

A force is needed to :

• Change the state of motion or state of rest of the body .

• Keep the body in motion

• keep the body stationary

• keep the velocity of body constant .

Exercise 3 (C) [Page 69]

### Selina solutions for Concise Physics Class 9 ICSE Chapter 3 Laws of Motion Exercise 3 (C) [Page 69]

Exercise 3 (C) | Q 1 | Page 69

Name the two factors on which the force needed to stop a moving body in a given time depends.

Exercise 3 (C) | Q 2 | Page 69

Define linear momentum and state its S.I. unit.

Exercise 3 (C) | Q 3 | Page 69

A body of mass m moving with a velocity v is acted upon by a force. Write an expression for change in momentum in each of the following cases: (i) When v << c, (ii) When v → c and (iii) When v << c but m does not remain constant. Here, c is the speed of light.

Exercise 3 (C) | Q 4 | Page 69

Show that the rate of change of momentum = mass × acceleration. Under what condition does this relation hold?

Exercise 3 (C) | Q 5 | Page 69

Two bodies A and B of same mass are moving with velocities v and 2v, respectively. Compare their (i) inertia and (ii) momentum.

Exercise 3 (C) | Q 6 | Page 69

Two balls A and B of masses m and 2 m are in motion with velocities 2v and v, respectively. Compare:

(i) Their inertia.

(ii) Their momentum.

(iii)  The force needed to stop them in the same time.

Exercise 3 (C) | Q 7 | Page 69

State the Newton's second law of motion. What information do you get from it?

Exercise 3 (C) | Q 8 | Page 69

How does Newton's second law of motion differ from the first law of motion?

Exercise 3 (C) | Q 9 | Page 69

Write the mathematical form of Newton's second law of motion. State the conditions if any.

Exercise 3 (C) | Q 10 | Page 69

State Newton's second law of motion. Under what condition does it take the form F = ma?

Exercise 3 (C) | Q 11 | Page 69

How can Newton's first law of motion be obtained from the second law of motion?

Exercise 3 (C) | Q 12.1 | Page 69

Draw a graph to show the dependence of acceleration on force for a constant mass.

Exercise 3 (C) | Q 12.2 | Page 69

Draw a graph to show the dependence of force on mass for a constant acceleration.

Exercise 3 (C) | Q 13 | Page 69

How does the acceleration produced by a given force depend on the mass of the body? Draw a graph to show it.

Exercise 3 (C) | Q 14 | Page 69

Name the S.I. unit of force and define it .

Exercise 3 (C) | Q 15 | Page 69

What is the C.G.S. unit of force? How is it defined?

Exercise 3 (C) | Q 16 | Page 69

Name the S.I. and C.G.S. units of force. How are they related?

Exercise 3 (C) | Q 17 | Page 69

Why does a glass vessel break when it falls on a hard floor, but it does not break when it falls on a carpet?

Exercise 3 (C) | Q 18.1 | Page 69

Use Newton's second law of motion to explain the following instance :

A cricketer pulls his hands back while catching a fast moving cricket ball .

Exercise 3 (C) | Q 18.2 | Page 69

Use Newton's second law of motion to explain the following instance :
An athlete prefers to land on sand instead of hard floor while taking a high jump .

Exercise 3 (C) [Page 70]

### Selina solutions for Concise Physics Class 9 ICSE Chapter 3 Laws of Motion Exercise 3 (C) [Page 70]

Exercise 3 (C) | Q 1 | Page 70

The linear momentum of a body of mass m moving with velocity v is  :

• v/m

• m/v

• mv

• 1/mv

Exercise 3 (C) | Q 2 | Page 70

The unit of linear momentum is :

• N s

• kg m s-2

•  N s-1

• kg2 m s-1

Exercise 3 (C) | Q 3 | Page 70

The correct form of Newton's second law is :

• F = (Δ"p")/(Δ"t")

• "F"= "m"(Δ"v")/(Δ"t")

• "F = v"(Δ"m")/(Δ"t")"

• F = mv

Exercise 3 (C) | Q 4 | Page 70

The acceleration produced in a body by a force of given magnitude depends on

• size of the body

• shape of the body

• mass of the body

• none of these

Exercise 3 (C) [Page 70]

### Selina solutions for Concise Physics Class 9 ICSE Chapter 3 Laws of Motion Exercise 3 (C) [Page 70]

Exercise 3 (C) | Q 1 | Page 70

A body of mass 5 kg is moving with velocity 2 m s-1. Calculate its linear momentum.

Exercise 3 (C) | Q 2 | Page 70

The linear momentum of a ball of mass 50 g is 0.5 kg m s-1. Find its velocity.

Exercise 3 (C) | Q 3 | Page 70

A force of 15 N acts on a body of mass 2 kg. Calculate the acceleration produced.

Exercise 3 (C) | Q 4 | Page 70

A force of 10 N acts on a body of mass 5 kg. Find the acceleration produced.

Exercise 3 (C) | Q 5 | Page 70

Calculate the magnitude of force which when applied on a body of mass 0.5 kg produces an acceleration of 5 m s-2.

Exercise 3 (C) | Q 6.1 | Page 70

A force of 10 N acts on a body of mass 2 kg for 3 s, initially at rest. Calculate : The velocity acquired by the body

Exercise 3 (C) | Q 6.2 | Page 70

A force of 10 N acts on a body of mass 2 kg for 3 s, initially at rest. Calculate : Change in momentum of the body.

Exercise 3 (C) | Q 7.1 | Page 70

A force acts for 10 s on a stationary body of mass 100 kg, after which the force ceases to act. The body moves through a distance of 100 m in the next 5 s. Calculate : The velocity acquired by the body

Exercise 3 (C) | Q 7.2 | Page 70

A force acts for 10 s on a stationary body of mass 100 kg, after which the force ceases to act. The body moves through a distance of 100 m in the next 5 s. Calculate : The acceleration produced by the force

Exercise 3 (C) | Q 7.3 | Page 70

A force acts for 10 s on a stationary body of mass 100 kg, after which the force ceases to act. The body moves through a distance of 100 m in the next 5 s. Calculate : The magnitude of the force

Exercise 3 (C) | Q 8 | Page 70

Figure shows the velocity-time graph of a particle of mass 100 g moving in a straight line. Calculate the force acting on the particle.
(Hint : Acceleration = Slope of the v-t graph)

Exercise 3 (C) | Q 9 | Page 70

A force causes an acceleration of 10 m s-2 in a body of mass 500 g. What acceleration will be caused by the same force in a body of mass 5 kg?

Exercise 3 (C) | Q 10 | Page 70

A force acts for 0.1 s on a body of mass 2.0 kg initially at rest. The force is then withdrawn and the body moves with a velocity of 2 m s-1. Find the magnitude of the force.

Exercise 3 (C) | Q 11 | Page 70

A body of mass 500 g, initially at rest, is acted upon by a force which causes it to move a distance of 4 m in 2 s, Calculate the force applied.

Exercise 3 (C) | Q 12 | Page 70

A car of mass 480 kg moving at a speed of 54 km h-1 is stopped by applying brakes in 10 s . Calculate the force applied by the brakes .

Exercise 3 (C) | Q 13.1 | Page 70

A car is moving with a uniform velocity 30 ms-1. It is stopped in 2 s by applying a force of 1500 N through its brakes. Calculate the following values : The change in momentum of car.

Exercise 3 (C) | Q 13.2 | Page 70

A car is moving with a uniform velocity 30 ms-1. It is stopped in 2 s by applying a force of 1500 N through its brakes. Calculate the following values :  The retardation produced in car.

Exercise 3 (C) | Q 13.3 | Page 70

A car is moving with a uniform velocity 30 ms-1. It is stopped in 2 s by applying a force of 1500 N through its brakes. Calculate the following values : The mass of car.

Exercise 3 (C) | Q 14 | Page 70

A bullet of mass 50 g moving with an initial velocity 100 m s-1 strikes a wooden block and comes to rest after penetrating a distance 2 cm in it. Calculate: (i) Initial momentum of the bullet, (ii) Final momentum of the bullet, (iii) Retardation caused by the wooden block and (iv) Resistive force exerted by the wooden block.

Exercise 3 (D), Exercise 3 (C) [Page 73]

### Selina solutions for Concise Physics Class 9 ICSE Chapter 3 Laws of Motion Exercise 3 (D), Exercise 3 (C) [Page 73]

Exercise 3 (D) | Q 1 | Page 73

State the usefulness of Newton's third law of motion .

Exercise 3 (C) | Q 2 | Page 73

State Newton's third law of motion.

Exercise 3 (D) | Q 3 | Page 73

State and explain the law of action and reaction. by giving two examples.

Exercise 3 (D) | Q 4.1 | Page 73

Name and state the action and reaction in the following case :

Firing a bullet from a gun

Exercise 3 (D) | Q 4.2 | Page 73

Name and state the action and reaction in the following case :
Hammering a nail

Exercise 3 (D) | Q 4.3 | Page 73

Name and state the action and reaction in the following case :

A book lying on a table

Exercise 3 (D) | Q 4.4 | Page 73

Name and state the action and reaction in the following case :

A moving rocket

Exercise 3 (D) | Q 4.5 | Page 73

Name and state the action and reaction in the following case :

A person moving on the floor

Exercise 3 (D) | Q 4.6 | Page 73

Name and state the action and reaction in the following case :

A moving train colliding with a stationary train

Exercise 3 (D) | Q 5 | Page 73

Explain the motion of a rocket with the help of Newton's third law.

Exercise 3 (D) | Q 6 | Page 73

When a shot is fired from a gun, the gun is recoiled. Explain.

Exercise 3 (D) | Q 7 | Page 73

When you step ashore from a stationary boat, it tends to leave the shore. Explain.

Exercise 3 (D) | Q 8 | Page 73

When two spring balances joined at their free ends are pulled apart, both show the same reading. Explain.

Exercise 3 (D) | Q 9 | Page 73

To move a boat ahead in water, the boatman has to push the water backwards by his oar. Explain this statement.

Exercise 3 (D) | Q 10 | Page 73

A person pushing a wall hard is liable to fall back. Give reason.

Exercise 3 (D) | Q 11 | Page 73

The action and reaction both act simultaneously. Is this statement true?

Exercise 3 (D) | Q 12 | Page 73

The 'Action and reaction are equal in magnitude'. Is this statement true?

Exercise 3 (D) | Q 13 | Page 73

A light ball falling on ground, after striking the ground rises upwards. Explain the reason.

Exercise 3 (D) | Q 14 | Page 73

Comment on the statement 'the sum of action and reaction on a body is zero'.

Exercise 3 (D) [Page 73]

### Selina solutions for Concise Physics Class 9 ICSE Chapter 3 Laws of Motion Exercise 3 (D) [Page 73]

Exercise 3 (D) | Q 1 | Page 73

Newton's third law :

• defines the force qualitatively

• Defines the force quantitatively.

• Explains the way the force acts on a body .

• Gives the direction of force.

Exercise 3 (D) | Q 2 | Page 73

Action and reaction act on :

• Same body in opposite directions.

• Different bodies in oppposite directions.

• Different bodies , but in the same direction.

• Same body in the same direction.

Exercise 3 (D) [Page 73]

### Selina solutions for Concise Physics Class 9 ICSE Chapter 3 Laws of Motion Exercise 3 (D) [Page 73]

Exercise 3 (D) | Q 1 | Page 73

A boy pushes a wall with a force of 10 N towards east. What force is exerted by the wall on the boy?

Exercise 3 (D) | Q 2 | Page 73

In the Figure a block of weight 15 N is hanging from a rigid support by a string. What force is exerted by (a) a block on the string and (b) a string on the block? Name and show them in the diagram.

Exercise 3 (E) [Pages 79 - 80]

### Selina solutions for Concise Physics Class 9 ICSE Chapter 3 Laws of Motion Exercise 3 (E) [Pages 79 - 80]

Exercise 3 (E) | Q 1 | Page 79

State Newton's law of gravitation.

Exercise 3 (E) | Q 2 | Page 79

State whether the gravitational force between two masses is attractive or repulsive ?

Exercise 3 (E) | Q 3 | Page 79

Write an expression for the gravitational force of attraction between two bodies of masses m1 and m2 separated by a distance r.

Exercise 3 (E) | Q 4 | Page 79

How does the gravitational force of attraction between two masses depend on the distance between them?

Exercise 3 (E) | Q 5 | Page 79

How is the gravitational force between two masses affected if the separation between them is doubled?

Exercise 3 (E) | Q 6 | Page 79

Define gravitational constant G.

Exercise 3 (E) | Q 7 | Page 79

Write the numerical value of gravitational constant G with its S.I. unit .

Exercise 3 (E) | Q 8 | Page 79

What is the importance of law of gravitation ?

Exercise 3 (E) | Q 9 | Page 79

What do you understand by the term force due to gravity ?

Exercise 3 (E) | Q 10 | Page 79

Write an expression for the force due to gravity on a body of mass m and explain the meaning of symbols used in it.

Exercise 3 (E) | Q 11 | Page 79

Define the term acceleration due to gravity? Write its S.I. unit.

Exercise 3 (E) | Q 12 | Page 79

Write down the average value of g on Earth's surface ?

Exercise 3 (E) | Q 13 | Page 79

How is the acccelaration due to gravity on the surface of the earth realted to its mass and radius ?

Exercise 3 (E) | Q 14 | Page 79

How are g and G realated ?

Exercise 3 (E) | Q 15 | Page 79

A body falls freely under gravity from rest and reaches the ground in time t. Write the expression for the height fallen by the body.

Exercise 3 (E) | Q 16 | Page 79

A body is thrown vertically upwards with an initial velocity u. Write the expression for the maximum height attained by the body.

Exercise 3 (E) | Q 17 | Page 79

Define the terms mass and weight.

Exercise 3 (E) | Q 18 | Page 79

Distinguish between mass and weight.

Exercise 3 (E) | Q 19 | Page 80

State the S.I. units of (a) mass and (b) weight.

Exercise 3 (E) | Q 20 | Page 80

The value of g at the centre of Earth is zero. What will be the weight of a body of mass m kg at the centre of the Earth?

Exercise 3 (E) | Q 21 | Page 80

Which of the following quantity does not change by change of place of a body : mass or weight ?

Exercise 3 (E) | Q 22 | Page 80

Explain the meaning of the following statement '1 kgf = 9.8 N'.

Exercise 3 (E) [Page 80]

### Selina solutions for Concise Physics Class 9 ICSE Chapter 3 Laws of Motion Exercise 3 (E) [Page 80]

Exercise 3 (E) | Q 1 | Page 80

The gravitational force between two bodies is :

• Always repulsive

• always attractive

• attractive only at large distance

• Repulsive only at large distance .

Exercise 3 (E) | Q 2 | Page 80

The value of G is :

• 9.8 N m2 kg-2

• 6.7 x 10-11 N m2 kg-2

• 6.7 x 10-11 m s-2

•  6.7 N kg-1

Exercise 3 (E) | Q 3 | Page 80

The force of attraction between two masses each of 1 kg kept at a separation of 1 m is :

• 9.8 N

• 6.7 N

• 980 N

• 6.7 × 10-11 N

Exercise 3 (E) | Q 4 | Page 80

A body is projected vertically upward with an initial velocity u . If acceleartion due to gravity is g , the time for which it remains in air , is :

• u/g

• ug

• (2u)/g

• u/(2g)

Exercise 3 (E) | Q 5 | Page 80

An object falling freely from rest reaches ground in 2 s. If acceleration due to gravity is 9.8 m s-2, then the velocity of object on reaching the ground will be

•  9.8 m s-1

• 4.9 m s-1

• 19.6 m s-1

• Zero

Exercise 3 (E) [Pages 80 - 81]

### Selina solutions for Concise Physics Class 9 ICSE Chapter 3 Laws of Motion Exercise 3 (E) [Pages 80 - 81]

Exercise 3 (E) | Q 1 | Page 80

The force of attraction between two bodies at certain separation is 10 N. What will be the force of attraction between them if the separation is reduced to half?

Exercise 3 (E) | Q 2 | Page 80

Write the approximate weight of a body of mass 5 kg. What assumption have you made?

Exercise 3 (E) | Q 3 | Page 80

Calculate the weight of a body of mass 10 kg in (a) kgf and (b) newton. Take g = 9.8 m s-2.

Exercise 3 (E) | Q 4 | Page 80

State the magnitude and direction of the force of gravity acting on the body of mass 5 kg. Take g = 9.8 m s-2.

Exercise 3 (E) | Q 5 | Page 80

The weight of a body is 2.0 N. What is the mass of the body? (g = 10 m s-2)

Exercise 3 (E) | Q 6 | Page 80

The weight of a body on Earth is 98 N, where acceleration due to gravity is 9.8 m s-2. What will be its (a) mass and (b) weight on the Moon, where acceleration due to gravity is 1.6 m s-2?

Exercise 3 (E) | Q 7 | Page 80

A man weighs 600 N on the Earth. What would be his approximate weight on the Moon? Give a reason for your answer?

Exercise 3 (E) | Q 8 | Page 80

What is the (a) force of gravity and (b) weight of a block of mass 10.5 kg ? Take g = 10 ms-2 .

Exercise 3 (E) | Q 9.1 | Page 80

A ball is released from a height and it reaches the ground in 3 s. If g= 9.8 m s-2 Find :
the height from which the ball was released

Exercise 3 (E) | Q 9.2 | Page 80

A ball is released from a height and it reaches the ground in 3 s. If g= 9.8 m s-2 Find :
the velocity with which the ball will strike the ground .

Exercise 3 (E) | Q 10 | Page 80

What force, in newton, your muscles need to apply to hold a mass of 5 kg in your hand? State the assumption.

Exercise 3 (E) | Q 11.1 | Page 80

A ball is thrown vertically upwards. It goes to a height 20 m and then returns to the ground. Taking acceleration due to gravity g to be 10 ms-2 , find :
the initial velocity of the ball

Exercise 3 (E) | Q 11.2 | Page 80

A ball is thrown vertically upwards. It goes to a height 20 m and then returns to the ground. Taking acceleration due to gravity g to be 10 ms-2 , find :
the final velocity of the ball on reaching the ground .

Exercise 3 (E) | Q 11.3 | Page 80

A ball is thrown vertically upwards. It goes to a height 20 m and then returns to the ground. Taking acceleration due to gravity g to be 10 ms-2 , find :
the total time of journey of the ball .

Exercise 3 (E) | Q 12 | Page 80

An body is dropped from the top of a tower. It acquires a velocity 20 m s-1 on reaching the ground. Calculate the height of the tower. (Take g = 10 m s-2)

Exercise 3 (E) | Q 13.1 | Page 81

A ball is thrown vertically upwards. It returns 6 s later. Calculate : The greatest height reached by the ball . (Take g = 10 m s-2)

Exercise 3 (E) | Q 13.2 | Page 81

A ball is thrown vertically upwards. It returns 6 s later. Calculate : the initial velocity of the ball (Take g = 10 m s-2)

Exercise 3 (E) | Q 14 | Page 81

A pebble is thrown vertically upwards with a speed of 20 m s-1. How high will it be after 2 s? (Take g = 10 m s-2)

Exercise 3 (E) | Q 15.1 | Page 81

How long will a stone take to fall to the ground from the top of a building 80 m high

Exercise 3 (E) | Q 15.2 | Page 81

What will be the velocity of the stone on reaching the ground? (Take g=10 m s-2)

Exercise 3 (E) | Q 16 | Page 81

A body falls from the top of a building and reaches the ground 2.5 s later. How high is the building? (Take g = 9.8 m s-2)

Exercise 3 (E) | Q 17.1 | Page 81

A ball is thrown vertically upwards with an initial velocity of 49 m s-1 .  calculate : the maximum height attained .

Exercise 3 (E) | Q 17.2 | Page 81

ball is thrown vertically upwards with an initial velocity of 49 m s-1. Calculate: The time taken by it before it reaches the ground again. (Take g = 9.8 m s-2).

Exercise 3 (E) | Q 18 | Page 81

A stone is dropped freely from the top of a tower and it reaches the ground in 4 s. Taking g = 10m s-2, calculate the height of the tower.

Exercise 3 (E) | Q 19.1 | Page 81

A pebble is dropped freely in a well from its top. It takes 20 s for the pebble to reach the water surface in the well. Taking g = 10 m s-2 and speed of sound = 330 m s-1. Find : The depth of water surface

Exercise 3 (E) | Q 19.2 | Page 81

A pebble is dropped freely in a well from its top. It takes 20 s for the pebble to reach the water surface in the well. Taking g = 10 m s-2 and speed of sound = 330 m s-1. Find : The time when echo is heard after the pebble is dropped.

Exercise 3 (E) | Q 20 | Page 81

A ball is thrown vertically upwards from the top of a tower with an initial velocity of 19.6 m s-1. The ball reaches the ground after 5 s. Calculate: (i) The height of the tower, (ii) The velocity of the ball on reaching the ground. Take g= 9.8 ms-2.

## Chapter 3: Laws of Motion

Exercise 3 (A)Exercise 3 (B)Exercise 2 (B)Exercise 3 (C)Exercise 3 (D)Exercise 3 (E)

## Selina solutions for Concise Physics Class 9 ICSE chapter 3 - Laws of Motion

Selina solutions for Concise Physics Class 9 ICSE chapter 3 (Laws of Motion) include all questions with solution and detail explanation. This will clear students doubts about any question and improve application skills while preparing for board exams. The detailed, step-by-step solutions will help you understand the concepts better and clear your confusions, if any. Shaalaa.com has the CISCE Concise Physics Class 9 ICSE solutions in a manner that help students grasp basic concepts better and faster.

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Concepts covered in Concise Physics Class 9 ICSE chapter 3 Laws of Motion are Newton's First Law of Motion, Newton’s Second Law of Motion, Newton's Third Law of Motion, Free Fall, Gravitational Units of Force, Newton’s Universal Law of Gravitation, Newton’s Second Law of Motion in Terms of Rate of Change of Momentum, Force Due to Gravity, Acceleration Due to Gravity (Earth’s Gravitational Acceleration), Mass and Weight of an Object, Effect of Force, Types of Force: Contact Force, Types of Force: Non-Contact Force, Inertia and Mass, Types of Inertia, Linear Momentum, Change in Momentum, Rate of Change of Momentum.

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