Question

A ball with a mass of `1 kg` and velocity of `5 m/s` collides with a second ball with a mass of `3 kg` and velocity of `- 2 m/s`. If `20%` of the kinetic energy is lost, what are the final velocities of the balls?

Answer 1

-0.20 m/s (Ball A reverses direction)

Explanation:

First we calculate the total momentum energy available. Then we calculate the result with no energy loss, and finally we apply the 20% energy reduction to both results.

Ball A: 1kg * 5m/s = 5 kg-m/s
Ball B: 3kg * -2m/s = -6 kg-m/s

Resultant: Both balls have momentum of -1 kg-m/s with a combined mass of 4 kg. Therefore the velocity is -0.25 m/s.
If 20% of the energy is lost, this is reduced to -0.20 m/s.