Here's the problem and I'm close to the answer, but I guess close isn't good enough on a Physics exam. A spinning solid disk, rotating with angular velocity Wo, is put down on a level surface. It slides and rolls until it reaches an angular velocity W at which it rolls without sliding. Show that W = Wo/3 I place my origin on the ground so that angular momentum is conserved. The disk spins clockwise 1 = right when the disk is placed on the floor. 2 = right when the disk begins rolling without spinning. L = angular momentum. cm = center of mass. I = moment of inertia about cm R = radius M = Mass V = Velocity of cm L1spin + L1cm = L2spin + L2cm IWo + 0 = IW - RMV ==> with no slip V = RW (2/5)MWoR^2 = (2/5)MWR^2 - MWR^2 -2Wo/3 = W Besides probably messing up the signs, why do I end up with twice what I need?