Question

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 1

Expression for kinetic energy 

Ek= ½ mv² 

m = Mass of object 

v = Velocity of the object in ms⁻¹ 

Given that kinetic energy, Ek=25J 

(i) If the velocity of an object is doubled, then v = 5 × 2 = 10 ms⁻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.80