1. On a table (defining the x,y-plane laying 3 identical coins A,B and C with identical diameter of 18.00mm. The coordinates of their centers are Z(0,0), Y(60.0,0), X(60.0, 45.0) all given in mm. Under what angle relative to the x-axis one has to push Z against Y so that Z performs after the collision with Y another central collision with X? Assume elastic collision, neglect friction. 2. m1(vi1 - vf1) = m2(vf2 - vi2) vi1 + vf1 = vf2 + vi2 3. The attempt at a solution 1. The problem statement, all variables and given/known data 2. Relevant equations 3. I really don't understand how to find the angle when we don't have the velocities.