A Level Physics Practice Exam

When a golf ball is dropped, how does its momentum affect the Earth during its fall?

1. The ball's momentum has no effect on Earth

2. Earth gains momentum equal to the ball's momentum

3. Earth moves in the same direction as the falling ball

4. The ball's downward momentum contributes to the Earth's upward momentum

The correct answer is: The ball's momentum has no effect on Earth

The correct understanding of momentum in this scenario hinges on the principle of conservation of momentum. When a golf ball is dropped, it begins to accelerate towards the Earth due to gravity. As it falls, the ball gains momentum, which is the product of its mass and velocity. According to the principle of conservation of momentum, when the ball is dropped, it causes a change in the momentum of the Earth as well. Though the Earth has a much greater mass compared to the golf ball, it does gain momentum, albeit imperceptibly small relative to the vast mass of the Earth. The momentum that the golf ball gains in its downward motion actually results in an equal and opposite change in the momentum of the Earth. As the ball falls down, the Earth indeed experiences a very tiny amount of upward momentum since momentum must be conserved in the system. The movement of the Earth is so minuscule due to its massive size compared to the ball’s relatively small mass that it is practically unnoticeable. Therefore, while it may seem that the ball's momentum has no effect, it actually does contribute to the total momentum of the Earth, leading to the conclusion about Earth's interaction with the ball during the fall. Choosing the option that states the ball's momentum has