1. The problem statement, all variables and given/known data A wooden block of mass M resting on a frictionless horizontal surface is attached to a rigid rod of length l and of negligible mass. The rod is pivoted at the other end. A bullet of mass m traveling parallel to the horizontal surface and perpendicular to the rod with speed v hits the block and becomes embedded in it. What fraction of the original kinetic energy is list in the collision? 2. Relevant equations KE = 1/2 m v^2 L = cross(r,p) 3. The attempt at a solution The only way I can think of doing this problem is using linear momentum conservation. Say if pi = m*v, pf = (m+M)v' v' = v * m / (M+m) final / initial Kinetic Energy = m / (M+m) Unfortunately, the answer is M/(M+m). I believe that I should be using conservation of angular momentum. According to part a of this problem (not stated) the angular momentum of the bullet+block = mvl. If I were to use cons. of angular momentum, I don't really know to formulate it. Initial Li = 0 Final Lf = mvl Does anyone have any hints?