# NCERT Class 9 Science Solutions: Chapter 11 – Work and Energy Part 2

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Question 1:

Q. What is the kinetic energy of an object?

Kinetic energy is the energy possessed by a body by the virtue of its motion. Every moving object possesses kinetic energy. A body uses kinetic energy to do work. Kinetic energy of hammer is used in driving a nail into a log of wood, kinetic energy of air is used to run wind mills, etc.

Question 2:

Q. Write an expression for the kinetic energy of an object.

If a body of mass is moving with a velocity then its kinetic energy is given by the expression,

Its SI unit is Joule

Question 3:

Q. The kinetic energy of an object of mass, moving with a velocity of is. What will be its kinetic energy when its velocity is double? What will be its kinetic energy when its velocity is increased three times?

Expression for kinetic energy is

Mass of the object

Velocity of the object

Given that kinetic energy,

If the velocity of an object is double, then. Therefore, its kinetic energy becomes times its original value, because it is proportional to the square of the velocity. Hence, kinetic energy

If velocity is increased three times, then its kinetic energy becomes times its original value, because it is proportional to the square of the velocity. Hence, kinetic energy.