Question

Describe the resulting behavior of a tennis ball if a force momentarily did positive work on the ball, then a smaller force consistently did negative work on the ball, as the ball moved downwards through the air. Be specific about changes to the total energy, the kinetic energy, and the potential energy of the ball.

Answer 1

When the tennis ball is struck hard , the positive work is done on the ball by the racket ( as the ball starts moving in the same direction as directed by the force ) , after this the frictional force ( air resistance ) consistently does negative work on the ball by slowing it down as the ball moves downwards through the air .

In this whole process, the total energy of the system remains conserved . Intially the ball had purely kinetic energy when struck by racket, but as the ball started ascending in air , it kinetic energy kept on changing into potential energy until the ball reached its maximum height where kinetic energy became zero and the ball posses purely potential energy. Once the ball reached the maximum height, it again started to move downwards and hence the whole of potential energy starts to convert into kinetic energy . During this whole process, a part of total energy possessed by the ball kept on decreasing to overcome the air resistance ( friction).