My first association with the topic title was the "Bounce"-physics in certain fighting games involving scantily clad females... but you're not programming one of those, are you? :-D
Anyway, I can't help you with your problem. Sorry.
But you should probably describe your problem in more detail. What kind of effect do you want to achieve?
Ball-bouncing like in Pong/Arkanoid? Or realistic ball-bouncing like throwing a ping-pong ball at a wall or on the ground?