1. The problem statement, all variables and given/known data [PLAIN]http://img686.imageshack.us/img686/8532/phyf.jpg [Broken] It is observed that the ball always bounces exactly once on each step. 2. Relevant equations s = ut + 1/2at^2 3. The attempt at a solution [PLAIN]http://img28.imageshack.us/img28/6678/abccz.jpg [Broken] So after resolving, horizontal velocity must be always constant as it bounces exactly once on each step and must be 0.30/t ms^-1 So, u*cos(theta) = v*cos(phi) = 0.30(1/t) And to find e, we form the equation e*u*sin(theta) = -v*sin(phi) I also find time t, for which the ball moves -0.20m vertically and 0.30m horizontally. Upwards as positive. Using s = ut + 1/2at^2 -0.20 = v*sin(phi)*t + 1/2(-9.81)(t^2) But I tried manipulating around and I just can't find e. Is something wrong with my method? Do I need to use momentum to calculate this question? Thank you.