1. The problem statement, all variables and given/known data The Problem is the following: We have a uniform disk of radius r laying still with its center at the origin. Two bullets, with equal mass m and negligible size are approaching the disk, both with trajectories paralell to the x axis and at distance h, -h from the y axis respectively where h<r. The velocities are v1 and v2 whre v2>v1. Both bullets remain stuck in the disk immediately without penetrating it. The question is now to solve for v1 and v2 in dependance of the angular velocity and the velocity of the disk after the collision. 2. Relevant equations mh(v1+v2)=(1/2 Mr^2 + (2mr^2))w 3. The attempt at a solution I can solve the question without problems using this relation, which is also used in the solution. mh(v1+v2)=(1/2 Mr^2 + (2mr^2))w where w is the angular velocity. What bothers me is 1. why can we just assume that the disk will rotate about its center( at least I think this has to be assumed based on the moment of inertia we are using), 2. If the disk does rotate about its center it seems to me that it will have to continuously slow down unless the connecting line between the impact points of the bullets goes through the center.