A heavy disk of radius R and mass m is attached at the 1/3-point of a uniform shaft of length L. The shaft is clamped to a rigid base at A and at C. The radis of the shaft is r, and it is made of a material whose shear modulus of elasticty is G. Letting the rotation angle theta be the displacement coordinate, determine the equation of motion of the disk. Neglect the thickness of the disk.