1. The problem statement, all variables and given/known data : A gun is fired from a moving platform and the ranges of the shot are observed to be R and S when the platform is moving forward or backward respectively with velocity V. Prove that the elevation of the gun is tan(inverse)[g(R - S) ^ 2 / 4V ^ 2(R + S)] 2. Relevant equations : The three equations of motion and the equation for relative velocity. 3. The attempt at a solution : I am too confused with the "relative" velocity part. In all probability,we have to obtain a relation between R and S. I have no idea about this problem.