A disk of radius R and mass M is spinning at an angular velocity ω0 rad/s. A non-rotating concentric disk of radius r and mass m drops on it from a negligible height (its translational kinetic energy from falling can be ignored), and the two rotate together. Find (a) the final ω of the two disks (b) the fraction of the initial kinetic energy left in the system.

A disk of radius R and mass M is spinning at an angular velocity ω0 rad/s. A non-rotating concentric disk of radius r and mass m drops on it from a negligible height (its translational kinetic energy from falling can be ignored), and the two rotate together. Find (a) the final ω of the two disks (b) the fraction of the initial kinetic energy left in the system.