1. The problem statement, all variables and given/known data From Kleppner and Kolenkow: A small cube of mass m slides down a circular path of radius R cut into a large block of mass M, as shown. M rests on a table, and both blocks move without friction. The blocks are initially at rest, and m starts from the top of the path. Find the velocity v of the cube as it leaves the block. Ans. clue. If m=M, v=√(gR) http://img390.imageshack.us/img390/5575/blocksbi2.jpg [Broken] 2. Relevant equations KE=(1/2)mv2 PE=mgh mivi=mfvf KEi=KEf 3. The attempt at a solution For m, initial energy PEm=mgR Just before m leaves block M, KEm=(1/2)mv2=mgR Thus, v=√(2gR). From here, I set up equations for conservation of momentum as well as kinetic energy. I then used substitution and tried to solve for the velocity of m as it leaves the block, M, but the algebra just isn't working out. Did I make a mistake?