# Homework Help: Rotational Energy

1. Dec 9, 2004

### king_naeem

A uniform spherical shell of mass, M=4.5 kg and radius R=8.5 cm can rotate about a vertical axis on frictionless bearings. A massless cord passes around the equator of the shell, over a pulley of rotational inertia I=3.0*10^-3 kg*m^2 and radius r=5.0 cm, and is attached to a small object of mass m=0.60 kg. There is no friction on the pulley's axle; the cord does not slip on the pulley. What is the speed of the object when it has fallen 82 cm after being released from rest? use energy considerations.

2. Dec 9, 2004

### king_naeem

this was my attempt but i'm not getting the right answer:

ok here is how to do it (i think) both the sphere and the pully will have angular speeds so you can figure out there angular momentum via L = Iw now the change in angular momentum of the system must equate to the change in potential energy. further more the angular speeds of the sphere and the pully are related by the relation between the circumferance of the pully and that of the equator of the s