A spool of mass \(M\) and rotational inertia \(I\) is mounted on a fixed, frictionless, horizontal axle. The spool consists of an inner hub of radius \(r\) and an outer disk of radius \(R\). A light string is wrapped around the inner hub. A block of mass \(m\) is attached to the free end of the string. The system is released from rest, and the block descends as the string unwinds without slipping on the inner hub.