A tennis ball is dropped on a horizontal smooth surface. It bounces back to its original position after hitting the surface. The force on the ball during the collision is proportional to the length of compression of the ball. Which one of the following sketches describes the variation of its kinetic energy K with time t most appropriately?

The velocity of ball while falling at any time t: v = at
Thus the kinetic energy of ball at any time t: KE = 1/2mv² = 1/2m(at)²
Thus KE vs t is an upward parabola.
After it strikes the surface, the whole kinetic energy converts to deformation potential energy in a small amount of time, and then the process reverts back.
The kinetic energy increases symmetrically to the loss earlier and then decreases parabolically. Thus correct representation is option B.