Question

A body of mass 10 kg is moving with a velocity 20 m s^-1. If the mass of the body is doubled and its velocity is halved, find the ratio of the initial kinetic energy to the final kinetic energy.

Answer 1

Let initial Mass, m₁= 10kg and velocity, v₁ = 20 m/s

Final mass, m₂ = 2 × 10 = 20 kg and velocity, v₂ = 20/2 = 10m/s

Initial kinetic energy, K₁= 1/2 x mass x (velocity)² 

= 1/2 ×10 ×(20)² 

= 12 ×10 ×20 ×20

= 2000 J

Final kinetic energy, K₂ = 1/2 x mass x (velocity)²