Question

select the correct answer. a tennis ball is hit into the air with a racket. when is the balls kinetic energy the greatest? ignore air resistance. a. when it leaves the racket b. just before it reaches the ground c. when it reaches its maximum height d. when its kinetic energy and potential energy are equal e. just before it starts falling downward

Explanation:

The total mechanical energy (sum of kinetic and potential energy) is conserved as air - resistance is ignored. Kinetic energy $K = \frac{1}{2}mv^{2}$ and potential energy $U = mgh$. At the ground level, the height $h$ is minimum, so the potential energy is minimum. Since the total energy $E=K + U$ is constant, when $U$ is minimum, $K$ is maximum. Just before the ball reaches the ground, its height is close to zero (minimum potential energy), so its kinetic energy is the greatest.

Answer:

B. just before it reaches the ground