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Homework Help: Cicrular/rotational dynamics

  1. Jul 22, 2011 #1
    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.


    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. jcsd
  3. Jul 22, 2011 #2
    Find the angular acceleration from another formula for torque (which also requires the moment of inertia)
  4. Jul 22, 2011 #3


    User Avatar

    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?
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