A cube of mass M = 500 g and side length 30 mm is free to spin on an axis through the center of one face. A massless pulley on this axis has a diameter of 2r = 10 mm. An object with m = 50 g is hung from a string wrapped around the pulley. The assembly is released from rest. Ignore friction.
What is the kinetic energy of the spinning block after the string unwinds? Use energy methods