A tennis player hits a tennis ball with a racket. Consider the system made up of the ball and the racket. Is the total momentum of the system the same just before and just after the hit? Is the total momentum just after the hit the same as 2 s later, when the ball is in midair at the high point of its trajectory? Explain any differences between the two cases.
Solution 17DQ Total momentum of a system remains constant only when no external force is applied on the system. Therefore, the total momentum of the system before and after hitting is not the same as during the hit, the racket exerts a force on the ball. If we consider the presence of air resistance when the ball is in midair, the ball will lose speed due to air drag. This lose in speed of the ball will result in a different momentum of the ball in midair than just after being hit.