A uniform circular ring of mass 4.0kg and radius 0.40m is suspended from a frictionless pin that passes through a point on its rim; the ring can rotate freely in a vertical plane about the pin. Initially the ring is at rest. A 0.30kg blob of putty moves horizontally at 5.0m/s and sticks to the point on the rim diametrically opposite the pin. Ignore any other forces during the brief impact.
(a) Compute the magnitude of the putty’s angular momentum about the pin just before it strikes.
(b) Determine the angular speed of the ring–putty system immediately after the putty sticks.
(c) A student instead calculated angular momentum about the center of the ring. Calculate that value and explain qualitatively why using it in part (b) would yield an incorrect angular speed.