Consider a rubber ball freely falling from a height h = 4.9 m onto a horizontal elastic plate. Assume that the duration of collision is negligible and the collision with the plate is totally elastic. Then the velocity as a function of time the height as function of time will be

Options

A.
B.
C.
D.

Answer

C

Explanation

As rubber ball is freely falling, the ball is dropped (u = 0). If we take downwards direction negative, the velocity at any time t can be given by the relation v = – gt. As when coming down, v increase, make collision, the value of v becomes + ve, the speed decreases, momentarily comes to zero and then moves in downwards direction and speed increases. The change from +ve to –ve is almost instantaneous.
Further `h = 1/2 gt^2` is a parabola which opens downwards.