Exercise-3D Laws of Motion Concise ICSE Class-9 Selina Publishers

Exercise-3D Laws of Motion Concise ICSE Class-9 Selina Publishers Solutions Chapter-3 . Step By Step ICSE Selina Concise Solutions of Chapter-3 Laws of Motion  with Exercise-3(A), Exercise-3(B) , Exercise-3(C) ,Exercise-3(D) and Exercise-3(E) including Numerical and MCQ Questions Solved Visit official Website CISCE for detail information about ICSE Board Class-9.

Board ICSE
Publications Selina Publication
Subject Physics
Class 9th
Chapter-3 Laws of Motion  Exe-3(D)
Book Name Concise
Topics Solution of  Exercise-3(A),  MCQ-3(A),      Exercise-3(B),  MCQ-3(B),    Exercise-3(C),  MCQ-3(C) ,Numericals-3(C),  Exercise-3(D),  MCQ-3(D),  Numericals-3(D)Exercise-3(E),  MCQ-3(E) ,  Numericals-3(E),
Academic Session 2021-2022

Exercise-3D Laws of Motion Concise ICSE Class-9 Selina Publishers Physics Chapter-3



–: Select Topics :–

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 Exercise-3(A),  MCQ-3(A),  

 Exercise-3(B),  MCQ-3(B)

Exercise-3(C),  MCQ-3(C) ,  Numericals-3(C),

Exercise-3(D),  MCQ-3(D) ,  Numericals-3(D),

Exercise-3(E),  MCQ-3(E) ,  Numericals-3(E),

Note :-  Before Viewing Selina Concise Physics Solutions of Chapter-3 Laws of Motion Class-9 Physics . Read the whole chapter carefully and Solved all example of Exercise-3 Laws of Motion Class-9 Physics


EXERCISE 3-(D) Chapter-3 Laws of Motion Class-9 Physics Selina Concise Solutions

Page 73

Question 1

State the Usefulness of Newton’s third law of motion.

Answer 1

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Newton’s third law explains how a force acts on an object.

Question 2

State Newton’s third law of motion.

Answer 2

According to Newton’s third law of motion, to every action there is always an equal and opposite reaction. The action and reaction act simultaneously on two different bodies.

Question 3  Exercise-3D Laws of Motion Concise ICSE

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

Answer 3  

Law of action and reaction: In an interaction of two bodies A and B, the magnitude of action, i.e. the force FAB applied by the body B on the body A, is equal in magnitude to the reaction, i.e., the force FBA applied by the body A on the body B, but they are in directions opposite to each other.

Examples of Law of action and reaction

(i) When a book is placed on a table, it does not move downwards. It implies that the resultant force on the book is zero, which is possible only if the table exerts an upward force of reaction on the book, equal to the weight of the book.

(ii) While moving on the ground, we exert a force by our feet to push the ground backwards; the ground exerts a force of the same magnitude on our feet forward, which makes it easier for us to move.

Explanation of Law of action and reaction

In the above stated example, there are two objects and two forces. the first example, the weight of the book acts downwards (action) and the force of the table acts upwards (reaction).

while In the second example, our feet exerts a force on the ground (action) and the ground exerts an equal and opposite force (reaction) on our feet.

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Question 4

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

(a) Firing a bullet from a gun,

 (b) Hammering a nail,

(c) A book lying on a table,

 (d) A moving rocket,

(e) A person moving on the floor,

(f) A moving train colliding with a stationary train.

Answer 4

(a) Action: Force exerted on the bullet.

Reaction: Recoil experienced by the gun.

(b) Action: The force exerted by the hammer on the nail.

Reaction: The force applied by the nail on the hammer.

(c) Action: Weight of the book acting downwards.

Reaction: Force acted by the table upwards.

(d) Action: Force exerted by the rocket on the gases backwards.

Reaction: Force exerted by outgoing gases on the rocket in forward direction.

(e) Action: Force exerted by the feet on the ground in backward direction.

Reaction: Force exerted by the ground on feet in forward direction.

(f) Action: Force exerted by a moving train on a stationary train.

Reaction: Force exerted by a stationary train on a moving train.

Question 5

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

Answer 5

When a rocket moves in space, it pushes gases outside, i.e. the rocket applies force on the gases in the backward direction. As a reaction, the gases put equal amount of force on the rocket in the opposite direction and the rocket moves in the forward direction.

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

Question 6  Exercise-3D Laws of Motion Concise ICSE

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

Answer 6

When a man fires a bullet from a gun, a force F is exerted on the bullet (action), and the gun experiences an equal and opposite recoil (reaction) and hence gets recoiled

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

Question 7

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

Answer 7

When a man exerts a force (action) on the boat by stepping into it, its force of reaction makes him step out of the boat, and the boat tends to leave the shore due to the force exerted by the man (i.e. action).

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

Question 8

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

Answer 8

Couple two spring balances A and B as shown in the figure. When we pull the balance B, both the balances show the same reading indicating that both the action and reaction forces are equal and opposite. In this case, the pull of either of the two spring balances can be regarded as action and that of the other balance as the reaction

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

Question 9

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

Answer 9

To move a boat, the boatman pushes (action) the water backwards with his oar. In this response, the water exerts an equal and opposite force (reaction) in the forward direction on the boat due to which the boat moves ahead.

Question 10

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

Answer 10

A person pushing a wall hard (action) by his palm, experiences a force (reaction) exerted by the wall on his palm in the opposite direction; thus, he is liable to fall backwards

Question 11 Laws of Motion Class-9 Physics Selina Solutions 

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

Answer 11

Yes, action and reaction act simultaneously.

Question 12

‘Action and reaction are equal in magnitude’. Is this statement true?

Answer 12

Yes, action and reaction are equal in magnitude.

Question 13

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

Answer 13

When a falling ball strikes the ground, it exerts a force on the ground. The ground exerts a force back at the ball in the opposite direction. This is the reason the ball rises upwards.

Question 14  Exercise-3D Laws of Motion Concise ICSE

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

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