A Disc with Moment of Inertia I₁ = 40 Kg $\omega$

Multiple Choice

A disc with moment of inertia I₁ = 40 kg.m² and angular velocity $\omega$ ₁ = 20 rad/s is dropped on to a stationary second disc along the axis of rotation.The second disc has moment of inertia I₂ = 60 kg.m².How much rotational kinetic energy is lost?

A) 3200 J
B) 4800 J
C) 8000 J
D) 11300 J
E) 15000 J