A circular disk of moment of inertia I, is rotating in a horizontal plane, its symmetry axis, with a constant angular speed wi. Another disk of moment of inertia I, is dropped coaxially onto the rotating disk. Initially the second disk has zero angular speed. Eventually both the disks rotate with a constant angular speed wf. The energy lost by the initially rotating disk to friction is: 1 (a): -w 2 (lt+lb) 1 (b) -w (lt+lb) Ib-It (c) -w (d) (It+lb) 1 Iblt 2 (lt+lb) W