Question:

A steel ball of mass $\displaystyle 73g$ is held above a horizontal steel plate, as illustrated in the figure below.

The ball is dropped from rest and it bounces on the plate, reaching a height h.

(a) Calculate the speed of ball as it reaches the plate.

(b) As the ball loses contact with the plate after bouncing, the kinetic energy of the ball is $\displaystyle 90\%$ of that just before bouncing. Calculate

(i) the height h to which the ball bounces.

(ii) the speed of the ball as it leaves the plate after bouncing.

(c) Using your answers to (a) and (b), determine the change in momentum of the ball during the bounce.

Attempt:

(a) $\displaystyle h = 1.6m \ , \ g = 9.81 ms^{-2}$

$\displaystyle \frac{1}{2}\not{m}v^2 = \not{m}gh$

$\displaystyle v = \sqrt{2gh}$

$\displaystyle v = \sqrt{2 \times 9.81 \times 1.6}$

$\displaystyle v = 5.6 ms^{-1}$

(b)(i) Don't know how to solve this this question... need help!