Exercise-3B 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(A) 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-3B Laws of Motion Concise ICSE Class-9 Selina Publishers Physics Chapter-3

–: Select Topics :–

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

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#### Question 1

Name the physical quantity that causes motion in a body.

Force causes motion in a body

#### Question 2

Is force needed to keep a moving body in motion?

Force is not needed to keep a moving body in motion.

#### Question 3

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

The force of friction between the table and the ball opposes the motion of the ball.

#### Question 4  Exercise-3B Laws of Motion Concise ICSE

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?

In absence of any external force, its speed shall remain unchanged.

#### Question 5

What is Galileo’s law of inertia?

Galileo’s law of inertia states that a body continues to be in its state of rest or of uniform motion unless an external force is applied on it.

#### Question 6

State Newton’s first law of motion.

According to Newton’s first law of motion, if a body is in a state of rest, it will remain in the state of rest, and if the body is in the state of motion, it will remain moving in the same direction with the same speed unless an external force is applied on it.

#### Question 7

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

Statement of Newton’s first law: If a body is in a state of rest, it will remain in the state of rest, and if the body is in the state of motion, it will remain moving in the same direction with the same speed unless an external force is applied on it.

Explanation: Newton’s first law can be explained in the following two parts:

##### (i) Definition of inertia:

The 1st part of Newton’s first law of motion gives the definition of inertia, according to which an object cannot change its state by itself.

Example: A book lying on a table will remain in its position unless it is displaced.

##### (ii) Definition of force:

The 2nd part of Newton’s first law defines force, according to which force is that external cause which can move a stationary object or which can stop a moving object.

Example: A book lying on a table is displaced from its place when it is pushed

#### Question 8  Exercise-3B Laws of Motion Concise ICSE

What is meant by the term inertia?

The property of an object by virtue of which it neither changes its state nor tends to change the state is called inertia.

#### Question 9

Give the qualitative definition of force based on Newton’s first law of motion.

Force is that external cause which can move a stationary object or which can stop a moving object.

#### Question 10

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

Inertia of a body depends on its mass. Inertia is directly proportional to mass, i.e. greater the mass of a body, greater is its inertia

#### Question 11

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

Examples to show that greater the mass, greater is the inertia of the body are as shown below:

(i) If you want to start a car by pushing it, you find that it takes a very large force to overcome its inertia. On the other hand, only a small force is needed to start a child’s express wagon. The difference between the car and express wagon is the difference in mass. The car has a large mass, whereas the wagon has a small one.

(ii) A cricket ball is more massive than a tennis ball. The cricket ball acquires a much smaller velocity than a tennis ball when the two balls are pushed with equal force for the same time.

#### Question 12

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

It is difficult, i.e. a larger force is required to set a loaded trolley (which has more mass) in motion than an unloaded trolley (which has less mass).

#### Question 13

Name the two kinds of inertia.

Two kinds of inertia are as listed below:

(i) Inertia of rest.

(ii) Inertia of motion.

#### Question 14  Exercise-3B Laws of Motion Concise ICSE

Give one example of each of the following :

(a) Inertia of rest, and

(b) Inertia of motion.

Examples of inertia of rest: A coin placed on top of a card remains in place when the card is slightly and quickly jerked horizontally.

Example of inertia of motion: A ball thrown vertically upwards by a person in a moving train comes back to his hand.

#### Question 15

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

No, the body will not move because the net force acting on it is zero. Hence, it will remain stationary due to inertia of rest.

#### Question 16

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

The motion remains unaffected because the net force acting on it is zero.

#### Question 17

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?

The net force on the airplane is zero or the upward force is equal to the downward force.

#### Question 18

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

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