A Level Physics Practice Exam

What is the effect on the Earth when a golf ball bounces off the ground?

1. The Earth moves significantly away

2. Both ball and Earth have zero momentum

3. The Earth gains momentum towards the ball

4. The Earth's momentum acts in the opposite direction to the ball

The correct answer is: The Earth's momentum acts in the opposite direction to the ball

When a golf ball bounces off the ground, both the ball and the Earth interact according to the principle of conservation of momentum and Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. As the golf ball strikes the ground and bounces back, it exerts a force on the Earth in the direction opposite to its initial motion. Consequently, the Earth experiences a tiny change in momentum in the opposite direction. Although this change is imperceptible due to the Earth's massive size compared to the golf ball, it is correct to say that the force exerted by the ball results in a corresponding momentum change of the Earth. Therefore, the statement that the Earth's momentum acts in the opposite direction to the ball accurately reflects this interaction. This choice correctly emphasizes the conservation of momentum in the system comprising both the golf ball and the Earth. Thus, even though the Earth's movement is negligible, it does gain a small amount of momentum towards the initial path of the ball.