A disk with radius = 0.5 m, mass = 6 kg, and I = 0.75 kg-m is released from rest at B and rolls down a 30° incline. An axle at the center of the disk is connected to point A by a spring with constant k = 10 N-m and unstretched length 0.5 m. Find the velocity of the center of the disk when it passes C.