A disk of moment of inertia 700. kg m2 is rotating in a horizontal plane

Question

A disk of moment of inertia 700. kg m² is rotating in a horizontal plane about an axis through its center with an angular speed of 11.0 rad/s. If a second, identical, but not rotating disk, is placed on top of the rotating disk, what will be the new rotation speed when the two disks rotate together?

𝜔_final =  ? rad/s

Answer 1

Conservation of Momentum requires that the L_i = L_f thus 700*11+700*0=700w_f*2. Solve to find w_f=5.5 rad/sec