Exercise-3E 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(E) Book Name Concise Topics Solution of  Exercise-3(D),  MCQ-3(D),  Numericals-3(D),    Exercise-3(E),  MCQ-3(E) ,  Numericals-3(E), Academic Session 2021-2022

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

–: Select Topics :–

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(E) Solutions of Selina Physics for ICSE Class-9 Laws of Motion

Page 79

#### Question 1

State Newton’s law of gravitation.

#### Answer 1 Newton’s law of gravitation

Every particle in the universe attracts every other particle with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them, and the direction of the force is along the line joining the masses.

#### Question 2

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

Gravitational force is always attractive.

#### Question 3

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

F∈ (Gm x M)/d²

Here G is a constant of proportionality called the universal gravitational constant.

#### Question 4  Exercise-3E Laws of Motion Concise

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

The gravitational force of attraction between two masses is inversely proportional to the square of distance between them.

#### Question 5

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

F∈ (Gm x M)/d²

If the distance between the masses becomes half, the force reduces to one-fourth.

#### Question 6

Define gravitational constant G.

The gravitational constant is defined as the force of attraction between two bodies of unit mass separated by a unit distance.

#### Question 7

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

The value of G in the S.I. system is 6.67 x 10-11Nm2kg-2.

#### Question 8

What is the importance of law of gravitation?

The gravitational force of attraction is significant to explain the motion of heavenly bodies, e.g. motion of planets around the Sun, motion of the Moon around the Earth etc.

#### Question 9

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

The force with which the Earth attracts a body towards its centre is called the force due to gravity.

#### Question 10

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

The force due to gravity on a body of mass m kept on the surface of Earth (mass=M and radius=R) is equal to the force of attraction between the Earth and that body.

F∈ (Gm x M)/d²

#### Question 11

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

The rate at which the velocity of a freely falling body increases is called acceleration due to gravity. Its S.I. unit is m/s2.

#### Question 12  Exercise-3E Laws of Motion Concise

Write down the average value of g on Earth’s surface.

The average value of ‘g’ on the Earth’s surface is 9.8 m/s2.

#### Question 13

How is the acceleration due to gravity on the Earth’s surface related to the mass and radius ?

Let g be the acceleration due to gravity on the Earth’s surface (mass = M and radius = R).

Then, g=gM/R²

#### Question 14

How are g and G related?

Acceleration due to gravity (g) is directly proportional to universal gravitational constant (G).

#### Question 15

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.

Initial velocity, u = 0.

Time taken = t.

Acceleration due to gravity = g.

Let ‘h’ be the height fallen.

#### Question 16

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

If a body is thrown vertically up with an initial velocity u to a height h, then there will be retardation (a = g).

At the highest point, the final velocity v = 0.

Thus, from the third equation, #### Question 17

Define the terms mass and weight.

Mass: The mass of a body is the quantity of matter it contains.

Weight: The weight of a body is the force with which the Earth attracts it.

#### Question 18 Laws of Motion Class-9 Physics Selina Solutions

Distinguish between mass and weight.

Mass is a scalar quantity, but weight is a vector quantity. It is the measure of the quantity of matter contained in a body, but weight is the measure of force with which the Earth attracts the body. While Mass of a body is always constant but weight varies from place to place.

Page 80

#### Question 19

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

#### Answer 19  Exercise-3E Laws of Motion Concise

The S.I. unit of mass is kg and that of weight is newton.

#### Question 20

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?

W = mg

At the centre of Earth, g = 0.

Therefore, W = 0.

#### Question 21

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

Mass of a body is always constant.

#### Question 22

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

1 kgf = 9.8 N.

One kilogramme force is the force due to gravity on a mass of 1 kilogramme

### MULTIPLE CHOICE TYPE-3(E) Laws of Motion Concise

Page 80

#### Question 1

The gravitational force between two bodies is :

(a) Always repulsive

(b) Always attractive

(c) Attractive only at large distances

(d) Repulsive only at large distances.

Always attractive

#### Question 2  Exercise-3E Laws of Motion Concise

The value of G is :

(a) 9.8 N m2 kg-2

(b) 6.7 x 10-11 N m2 kg-2

(c) 6.7 x 10-11 m s-2

(d) 6.7 N kg-1

6.7 x 10-11 N m2 kg-2

#### Question 3

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

(a) 9.8 N

(b) 6.7 N

(c) 980 N

(d) 6.7 x 10-11 N

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