The ball's kinetic energy is maximum when it leaves the racket.
Explanation:
The kinetic energy is given by KE= 1/2 mv²
Now when the tennis ball is hit by the racket, its velocity is maximum at that time. The velocity of the ball will decrease continuously because of the gravity as the ball goes up. The velocity of the ball is zero at the highest point.
So the velocity of the tennis ball is maximum when it leaves the racket. So the kinetic energy of the tennis ball is maximum when it leaves the racket.
How does each sum relate to the energy of the absorbed photon? the total energy of each set of emitted photons is equal to the energy of the absorbed photon.