1. The problem statement, all variables and given/known data Now,I am making the real game.The user can control the bat to hit the ball. Please look at this picture. Assume m2 is the bat and m1 is the ball The bat has its angle and its velocity vector(x,y). I want to find final velocity of the ball. I know the vector(x,y) of v1,v2 ,angle of the bat. I can't use this formular : m1v1+m2v2 = m1v1f+m2v2f and the formula for the conservation of kinetic energy (v1f is the final velocity of the ball) because the picture left and right have the same value of v1,v2.so they will have the same v1f. 2. Relevant equations 3. The attempt at a solution I try to find the normal of the bat and calculate it .follow by this picture. Sorry,The Picture is not correct; I use this formular : v1f = vv+v2 But it's not good How can I find the final velocity of the ball? Please give me some solution.