A light, horizontal rod of length 1.0 m is free to rotate without friction about a…
PHYSICS · Multi-part · AP · Physics C: Mechanics · Energy and Momentum of Rotating Systems · Energy and Momentum of Rotating Systems
Problem
A light, horizontal rod of length 1.0 m is free to rotate without friction about a vertical axis through its midpoint. The rod’s own mass is negligible. A small 0.40-kg slider can move without friction along the rod. A thin metal disk of mass 2.0 kg and radius 0.20 m is rigidly attached to the center of the rod so that it shares the same axis of rotation. At time t=0 the entire system is rotating at 4.0 rad/s, and the slider is located 0.15 m from the axis. Beginning at t=0, a light spring pulls the slider steadily outward so that its distance from the axis increases at a constant rate of 0.040 m/s. Neglect any motion of the slider other than its increasing radius.
(a) Compute the total angular momentum of the system about the axis at t=0.
(b) Determine the total angular momentum of the system 3.0 s after t=0.
(c) Is angular momentum conserved for the rod–disk–slider system during the 3.0-s interval? Justify your answer, clearly identifying any external torques that may act.