# Laws of Motion Exe-3C Very Short Answer Physics Class-9 ICSE Selina Publishers

Laws of Motion Exe-3C Linear Momentum Newton’s Second Law Very Short Answer Type for Class-9 ICSE Concise Physics. There is the solutions of Very short Answer type Questions of your latest textbook which is applicable in 2023-24 academic sessionVisit official Website CISCE for detail information about ICSE Board Class-9.

## Laws of Motion Exe-3C Linear Momentum Newton’s Second Law Very Short Answer

(ICSE Class – 9 Physics Concise Selina Publishers)

 Board ICSE Class 9th Subject Physics Writer / Publication Concise selina Publishers Chapter-3 Laws of Motion Exe – 3C Linear Momentum Newton’s Second Law Topics Solution of Exe-3(C) Very Short Answer Type Academic Session 2023-2024

### Exe-3C Linear Momentum Newton’s Second Law Very Short Answer Type

Ch-3 Laws of Motion Physics Class-9 ICSE Concise

Page 77

#### Question 1. Define linear momentum and state its S.I. unit.

Linear momentum of a body is the product of its mass and velocity.

Its SI unit is kgms-1.

#### Question 2. 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.

(i)  When  <<c,

p =  (mv) = mv

(ii) When v →c

p =  (mv)

(iii) When v << c but does not remain constant.

p =  (mv)

#### Question 3.Two bodies A and B of same mass are moving with velocities v and 2v, respectively. Compare their (i) inertia and (ii) momentum.

(i) Mass is the measure of inertia.

Let ‘m’ be the mass of the two bodies.

Inertia of body A:Inertia of body B :: m:m

Or, Inertia of body A:Inertia of body B :: 1:1

(ii)

Momentum of body A = m (v)

while Momentum of body B = m (2v) = 2mv

hence Momentum of body A:Momentum of body B :: mv:2mv

Or, Momentum of body A:Momentum of body B :: 1:2.

#### Question 4. 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.

(i) Inertia of body A:Inertia of body B :: m:2m

Or, Inertia of body A:Inertia of body B :: 1:2.

(ii)

Momentum of body A = m ( 2v) = 2mv

and Momentum of body B = (2m) v = 2mv

Hence Momentum of body A:Momentum of body B :: 2 mv:2mv

Or, Momentum of body A:Momentum of body B :: 1:1.

(iii) According to Newton’s 2nd law of motion, rate of change of momentum is directly proportional to the force applied on it. Therefore,

Force needed to stop A:Force needed to stop B :: 1:1.

(Laws of Motion Exe-3C Very Short Class-9 ICSE)

#### Question 5. Name the S.I. unit of force and define it.

The S.I. unit of force is newton.

One newton is the force which acts on a body of mass 1kg and produces an acceleration of 1 m/s2, i.e. 1 N = 1 kg × 1 m/s2.

#### Question 6. What is the C.G.S. unit of force? How is it defined?

The C.G.S. unit of force is dyne.

One dyne is the force which acts on a body of mass 1 gramme and produces an acceleration of 1 cms-2, i.e. 1 dyne = 1 g × 1 cms-2.