1. The problem statement, all variables and given/known data A boy sits on top of an igloo shaped like a semi-circle of Radius R. He begins to slide down the semi-circle. At what height above the ground does the boy slide off the semi-circle? Assume g=9.8 m/s2, and no friction. http://img207.imageshack.us/img207/4010/probmd1.jpg [Broken] 2. Relevant equations Conservation of energy? Or centrifugal force? 3. The attempt at a solution Couldn't think of any starting points; tried conservation of energy, but failed. Answer is obviously in terms of R. Can anyone shed the light on this problem?