Final answer:
The change in velocity of a tennis ball thrown at a wall in a collision is calculated by subtracting its initial velocity from its final velocity. If the ball is thrown at 3 m/s to the right and rebounds at 2 m/s to the left, the change in velocity is -5 m/s, indicating a direction reversal.
Step-by-step explanation:
When a ball is thrown at a wall and undergoes a collision, the change in velocity can be determined by comparing the ball's velocity just before impact and just after it rebounds. Assuming a tennis ball is thrown horizontally towards a wall at an initial velocity (u) of 3 m/s to the right, and after striking the wall, it returns at 2 m/s to the left, the change in velocity (Δv) would be calculated as follows:
Δv = v_final - v_initial
Since the direction changes after the collision, we consider the velocity after rebound as negative relative to the initial direction. Therefore:
Δv = (-2 m/s) - (3 m/s) = -5 m/s
The negative sign indicates that the velocity has reversed direction. The magnitude of this change in velocity is 5 m/s. It must be noted that a negative change does not imply a decrease in speed but a reversal in direction. The momentum change would be in the negative x-direction (or to the left), which implies the wall exerted a force in that same direction during the collision.