Short Answer. A solid disk rotates at a constant $7ra\frac{d}{s}.$ A hollow sphere, initially not spinning, is dropped onto the solid disk such that their axes coincide. After the collision, the two objects rotate as one. Assume the disk and the hollow sphere have the same mass $(300$ g $)$ and radius $(20cm).$ Calculate the angular speed immediately after the collision. You may assume that no external torques were applied during the collision.