Question

Consider a rubber ball freely falling from a height h = 4.9m 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 and the height as function of time will be

Answer 1

(c) : v = u + gt. As the ball is dropped, v = gt when coming down. v increases makes collision, the value of v becomes +ve, decreases comes to zero and increases. The change from +v to –v is almost instantaneous. Using –ve signs when coming down, (c) is correct.
Further h = (1/2)gt²  is a parabola. Therefore (c).