Problem Statement: The system consists of a 20-lb disk A, 4lb slender rod BC, and a 1-lb smooth collar C. If the disk rolls without slipping, determine the velocity of the collar at the instant theta=30 degrees. The system is released from rest when theta= 45 degrees. Above I attached a photo of what my FBD for the question looks like. When solving the question, the velocity of point B was described as 1.5*w(bc). I understand that the velocity of of any point of a rotating body is the angular speed times the radius, so where is the radius measured from? The rod is rotating about Point B isn't it?