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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.

Answer:

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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