1. The problem statement, all variables and given/known data A person of mass M is standing at one end of a board of mass m and length l. The board rests upon frictionless ice surface, and its mass is uniformly distributed along its length. The person now walks to the center of the board and stops. In terms of the given quantities, M, m and l, how far from his starting position relative to the ice surface has he moved? Note that there are no external forces acting on the system, only internal forces. 2. Relevant equations 3. The attempt at a solution I am not sure how to determine how the system will move. I have determined where the center of mass of the person-board system is, and I suspect it will enter the solution, but I can't figure anything out at the moment.