A circular disc of moment of inertia `I_t`, is rotating ina horizontal plane about its symmetry axis with a constant angular speed `omega`, Another disc of of moment of inertia `I_b`, is dropped coaxially onto the rotating disc. Initially the second disc has zero angular speed. Eventually both the discs 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_i^2`
B. `(1/2)(IbI_t)/(I_t + I_b) omega_i^2`
C. `(1/2)(I_t + I_b)/(I_t + I_b) omega_i^2`
D. `(I_b - I_t)/(I_t + I_b) omega_i^2`