Conservation of Angular Momentum: a Record Is Dropped Vertically onto a Freely

Multiple Choice

Conservation of angular momentum: A record is dropped vertically onto a freely rotating (undriven) turntable. Frictional forces act to bring the record and turntable to a common angular speed. If the rotational inertia of the record is 0.54 times that of the turntable, what percentage of the initial kinetic energy is lost?

A) 35%
B) 18%
C) 46%
D) 60%