Question

A ball of mass 4 kg travelling at 10 m/s makes an elastic head-on collision with another ball of mass 1 kg which is at rest. After the collision, the speed of the lighter ball is

*
zero
less than 10 m/s
equal to 10 m/s
greater than 10 m/s .

Answer 1

less than 10 m/s

Step-by-step explanation:

The 1 kg ball moves after the elastic collision, so you know its speed is > 0.

Due to the law of conservation of momentum, you know the total momentum before the collision must equal the total momentum after the collision. Some of the momentum from the 4 kg ball transfers to the 1 kg ball (which is at rest) when they collide. The 4 kg ball slows down after the collision and the lighter ball moves after the collision, but at a speed less than 10 m/s.