A block of mass \(M\) is placed on a horizontal, frictionless table and connected by a light string to a second block of mass \(2M\) that hangs vertically. The string passes over a pulley of mass \(M\) and radius \(R\) that is shaped like a uniform disk. The rotational inertia of a uniform disk is \(I = \dfrac{1}{2}MR^2\). The string does not slip on the pulley, and the pulley rotates with negligible friction about its central axle. The magnitude of the angular acceleration of the pulley is