# Homework Help: Cicrular/rotational dynamics

1. Jul 22, 2011

### jy1231

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

A solid cylinder of mass 10 kg is pivoted about a frictionless axis through the center O. A rope wrapped around the outer radius R1 = 1.0 m, exerts a force F1 = 5.0 N to the right. A second rope wrapped around another section of radius R2 = 0.50 m exerts a force F2 = 6.0 N downward. How many radians does the cylinder rotate through in the first 5.0 seconds, if it starts from rest?

2. Relevant equations

3. The attempt at a solution

I did find the torque for each force, with the counterclockwise force being positive.

so

T(1) = (1.0 m)(5m) = 5 N*m
T(2) = (0.5 m)(6.0 N) = 3 N*m

so I figured out that the net torque would be 2 N*m in the clockwise direction.

But i don't know what to do with this.

Thank you so much!

Sorry, here's the picture: http://tinypic.com/view.php?pic=otlszm&s=7

Last edited: Jul 22, 2011
2. Jul 22, 2011

### Pi-Bond

Find the angular acceleration from another formula for torque (which also requires the moment of inertia)

3. Jul 22, 2011

### Staff: Mentor

Hmm. Was there a diagram to accompany this problem? How are we to know if the ropes are wrapped in the same direction?