(3 points) A disk is spinning freely with angular speed 6.0 rad/s when a second identical disk, initially not spinning, is dropped on it so that their axes coincide. In a short time the two disks are co-rotating. a) Sketch the initial situation and the consequential situation. b) What is the angular speed of the new system? c) If a third such disk is dropped on the first two, find the final angular speed of the system.