Page No 152: - Chapter 11 Work & Energy class 9 ncert solutions Science - SaraNextGen [2024-2025]

Updated By SaraNextGen

On April 24, 2024, 11:35 AM

Question 1:

What is the kinetic energy of an object?

Answer:

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:

Write an expression for the kinetic energy of an object.

Answer:

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

Its SI unit is Joule (J).

Question 3:

The kinetic energy of an object of mass, m moving with a velocity of 5 m s⁻¹ is 25 J. What will be its kinetic energy when its velocity is doubled? What will be its kinetic energy when its velocity is increased three times?

Answer:

Expression for kinetic energy is 

m = Mass of the object

v = Velocity of the object = 5 m s⁻¹

Given that kinetic energy,   = 25 J

(i) If the velocity of an object is doubled, then v = 5 × 2 = 10 m s⁻¹.

Therefore, its kinetic energy becomes 4 times its original value, because it is proportional to the square of the velocity. Hence, kinetic energy = 25 × 4 = 100 J.

(ii) If velocity is increased three times, then its kinetic energy becomes 9 times its original value, because it is proportional to the square of the velocity. Hence, kinetic energy = 25 × 9 = 225 J.