A Small Rock Bounces Off a Moving Car and Change in Momentum

How does the car’s momentum change when a small rock bounces off the windshield of a moving car?

Which of Newton’s laws of motion states that an object at rest stays at rest and an object in motion stays in motion unless acted upon by an unbalanced force?

Answer:

When a rock bounces off a moving car, both the rock and the car experience a change in momentum. The car's momentum changes in the opposite direction to the rock's momentum.

Explanation

When a small rock bounces off the windshield of a moving car, both the rock and the car experience a change in momentum. According to Newton's third law of motion, for every action, there is an equal and opposite reaction. The change in momentum of the rock will be equal in magnitude but opposite in direction to the change in momentum of the car. Therefore, the car will have a change in momentum equal to that of the rock, in the opposite direction.

The law of motion that states an object at rest stays at rest and an object in motion stays in motion with the same speed and direction unless acted upon by an unbalanced force is Newton's first law of motion. This law is also known as the law of inertia.