일반물리학 1 — Rolling, Torque, and Angular Momentum: Problem 52

52 A cockroach of mass $m$ lies on the rim of a uniform disk of mass $4.00m$ that can rotate freely about its center like a merry-go-round. Initially the cockroach and disk rotate together with an angular velocity of $0.320\text{ rad/s}$. Then the cockroach walks halfway to the center of the disk. (a) What then is the angular velocity of the cockroach-disk system? (b) What is the ratio $K/K_0$ of the new kinetic energy of the system to its initial kinetic energy? (c) What accounts for the change in the kinetic energy?