1. The problem statement, all variables and given/known data A small block with mass m is moving towards a stationary slope with velocity v, angle θ and height h, suppose all surfaces are frictionless. Suppose the slope has mass M and it is able to move freely on the ground, what is the minimum initial speed for the block to be able to reach the top of the slope? 2. Relevant equations ΣPi = ΣPf ΔK = -ΔU 3. The attempt at a solution Case 1: Does the block travel up the wedge at v the moment it meets the wedge? If so, ΣPi in the horizontal axis is mvcosθ if I use the moment of transition of the block going up the wedge as the initial state. Case 2: However I could also use the initial state when the block have not meet the wedge for my initial momentum, thus ΣPi = mv. I'm confused because the answer for this question is vmin = √[(2gh)(M+m)/(M+msinθ)]. I will get this answer if I use case 1, and not case 2. But case 2 seems right too, but the answer I will get does not involve θ.