Please Help

[DR33]

A tennis ball is dropped from 5m High and bounces back 3.2 m high. It stays in contact with the floor for 0.036 seconds. What's the acceleration when it contacts the floor????

The answer is 495 m/s_². I just don't know how to get to it. thx so much.

[Tron3k]

Let v_1 be the speed of the ball just before it hits the ground, and v_2 be the speed just after.

Using energy:

mg(5) = \frac{1}{2} m v_1^2
10g = v_1^2
v_1 = \sqrt{10g}

Also:
mg(3.2) = \frac{1}{2} m v_2^2
6.4g = v_2^2
v_2 = \sqrt{6.4g}

Acceleration is the change in velocity divided by time. (Now consider the up direction to be positive)

a = \frac{\Delta v}{\Delta t}
a = \frac{\sqrt{6.4g} - (-\sqrt{10g})}{0.036}
a = 495 m/s^2

[DR33]

Thx so much.. I really appreciate people helping on other'S request.
thx again

l8er