A Level Physics Practice Exam

What happens to the momentum of a bouncing ball after impact with the ground?

1. It becomes zero

2. It reverses direction

3. It continues downward

4. It remains constant

The correct answer is: It reverses direction

When a ball bounces off the ground, its momentum undergoes a significant change. Initially, as the ball descends towards the ground, it possesses downward momentum due to its mass and velocity in the downward direction. Upon impact with the ground, a force is exerted by the ground on the ball, causing it to decelerate and eventually stop momentarily before reversing its velocity. As the ball travels upward after the bounce, its momentum is now in the opposite direction – upwards. Although the magnitude of the velocity and therefore the momentum may change depending on factors like energy loss during the bounce (due to factors like sound, heat, etc.), the direction of momentum definitely reverses as a result of the interaction with the ground. This change from downward momentum to upward momentum is the key feature of a bounce. Thus, the correct response highlights the important concept of momentum change upon impact, indicating not just a stop but also a complete reversal in direction, which is a fundamental aspect of elastic collisions such as a ball bouncing off a hard surface.