Hello. I have an exercise (not exactly homework, it's a physics contest that we are allowed to solve at home, using all possible help we can find) that goes like this: A ball with mass m = 0,10 kg falls vertically on a horizontal non-movable solid surface. Speed of the ball just before the contact with the surface was v0=14m/s. The time of contact of the ball and the surface during the bounce was τ = 4.0x10-3. I am to calculate the speed of the ball after the bounce. These are all information given (the only other instruction is to consider the surface, which is some kind of board, to be much more massive than the ball, and to consider the ball a perfectly elastic object). I'm not asking for a complete solution, but I would really use some help on what to do with the time of contact with surface, as I've never seen an exercise with this given (and Internet searc didn't reveal any usable equations for this particular problem). What is the theory behind this and what equation should I use? Thanks for any help.