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:

1. the initial kinetic energy, and
2. the final kinetic energy.

Answer 1

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

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

Initial kinetic energy, K₁= `1/2 × mv^2`

= `1/2 ×10 ×(20)^2`

= `1/2 × 10 × 20 × 20`

= 2000 J

Final kinetic energy, K₂ = `1/2 × mv^2`

= `1/2 × 20 ×(10)^2`

= `1/2 × 20 ×10 ×10`

= 1000 J

`"K"_1/"K"_2=2000/1000=1/2=2:1`