A phonograph record is dropped onto a freely spinning turntable.Then:
A)neither angular momentum nor mechanical energy is conserved because of the frictional forces between record and turntable
B)the frictional force between record and turntable increases the total angular momentum
C)the frictional force between record and turntable decreases the total angular momentum
D)the total angular momentum remains constant
E)the sum of the angular momentum and rotational kinetic energy remains constant

Question

Quizplus · Accepted Answer

When the phonograph record is dropped onto a freely spinning turntable, the system experiences no external torque, and hence, the total angular momentum remains conserved. The frictional force between the record and turntable may cause a transfer of some mechanical energy from rotational kinetic energy to heat, but the total mechanical energy may remain constant if there are no other external forces acting on the system. Therefore, option D is the correct choice.

A Phonograph Record Is Dropped onto a Freely Spinning Turntable