Lakhmir Singh Solutions Class 9 Physics Solutions for Exercise in Chapter 4 - Work And Energy

Question 54 Exercise

a) Define the term ‘energy’ of a body. What is the SI unit of energy.

b) What are the various forms of energy?

c) Two bodies having equal masses are moving with uniform speeds of v and 2v respectively. Find the ratio of their kinetic energies.


a) Energy is defined as the ability to do work and joule is the SI unit of energy.

b) Following are the various forms of energy:

Kinetic energy, potential energy, nuclear energy, electrical energy, chemical energy, sound energy, light energy, and heat energy.

c) Let the mass of both the bodies be m

Velocity of body 1, v1 = v

Velocity of body 2, v2 = 2v

KE1 = 1/2mv^2 = 1/2mv^2

KE2 = 1/2mv^2= 1/2mv_2^2

Ratio = KE1 : KE2 = 1/4

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