18-42. The system consists of a 10-kg disk A, 2-kg slender rod BC, and a 0.5 kg smooth collar C. If the disk rolls without slipping, determine the velocity of the collar at the instant 0=30°. The system is released from rest when 0 = 45°. 18-51. A spring having a stiffness of k = 300 N/m is attached to he end of the 15-kg rod, and it is unstretched when 0 = 0°. e released from root when B 0.24 m M 0.9 m A 8