# Kinetic Energy Numericals Class 9

**Question 1) A car is moving with a uniform velocity of 15 ms ^{-1}. What is the kinetic energy of a boy of mass 40 kg sitting in the car?**

Solution: Velocity of the boy = velocity of the car = v = 15 m/s

Here, the mass of the boy m = 40 kg.

Kinetic energy possessed by the boy = (1/2) mv^{2}= (1/2). 40. 15^{2}= 4500 J

**Question 2) If two bodies of equal masses move with uniform velocities of ‘v’ and ‘3v’, what will be the ratio of their kinetic energies?**

Mass of first body = m

The velocity of the first body = v

Mass of second body = m

The velocity of the second body = 3v

The ratio of kinetic energies of the two bodies

= Kinetic energies of the first body / Kinetic energy of the second body

=[ (1/2) mv^{2} ]/[ (1/2) m (3v)^{2} ] = v^{2} / 9 v^{2} = 1/9

The ratio of the kinetic energies = 1**:**9