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.What is the angular velocity of the two discs?

A) 4 rad/s
B) 6 rad/s
C) 8 rad/s
D) 12 rad/s
E) 20 rad/s