A circular disk of moment of inertia `I_t` is rotating in a horizontal plane, about its symmetry axis,with a constant angular, speed `omega_1` Another disk of moment of inertia `I_b` 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 `omega_f` The energy lost by the initially rotating disc to friction is :

Options

A. `1/2 (I_b^2)/((I_t+I_b)omega_1^2`
B. `1/2 (I_t^2)/((I_t+I_b)omega_1^2`
C. `(I_b-I_t)/((I_t+I_b))omega_1^2`
D. `1/2(I_bI_t)/((I_t+I_b))omega_1^2`