# Monkey on a Rotating Cylinder

1. Jan 10, 2010

### Dr Meow

1. The problem statement, all variables and given/known data

A 13-kg solid steel cylinder with a 10-cm radius is mounted on bearings so that it rotates freely about a horizontal axis. Around the cylinder is wound a number of turns of a fine gold thread. A 4.0-kg monkey named Fred holds on to the loose end and descends on the unwinding thread as the cylinder turns. Compute Fred's acceleration and the tension in the thread.

2. Relevant equations
Acceleration: a= Vf-Vo
t
Tension Moving Down: Ft = Fg + ma

3. The attempt at a solution

2. Jan 10, 2010

### JaWiB

What, no attempt at a solution? You're also going to need the moment of inertia of the cylinder, I believe

3. Jan 10, 2010

### Dr Meow

Sorry, my attempts at a solution only led me to the fact that Tension=MfG-MfA and then Tension=1/2McA and therefore MfG-MfA=1/2McA. "A" being acceleration, Mf being Mass of Fred, and Mc being mass of the cylinder and G being gravity.

4. Jan 11, 2010

### JaWiB

Tension=1/2McA

Where did this come from? You should be able to relate the tension to the torque on the cylinder and to its angular acceleration.

5. Jan 11, 2010

### Oktane

Don't you have to keep more in mind than just the torque and tension? Such as gravity? I'm not sure how those would fit together.

6. Jan 11, 2010

### JaWiB

Yes, the last piece of the problem should be relating the angular acceleration of the cylinder to the acceleration of the monkey (and the forces on the monkey)