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Homework Help: Help with pulleys and torque

  1. Nov 14, 2007 #1
    1. The problem statement, all variables and given/known data

    A rope passes over a 10-cm-diameter, 2.0 kg pulley that rotates on frictionless bearings. A graph shows the pulley's angular velocity as a function of time. The graph increases from (0,0) up to (3,120) linearly. Basically, there is a pulley with a rope thrown over it such that there are two sides to the rope, and two separate tensions, T_L (on the left side of the pulley), and T_R (on the right)

    a) Is the tension T_L in the left rope larger, smaller, or equal to the tension in the right rope? Explain.

    b) If you answered "equal" in part a, what is the magnitude of the tension T_L? If you answered "larger" or "smaller" in part a, what is the difference abs(T_L - T_R) between the two tensions?

    2. Relevant equations

    T = mr^2*alpha

    3. The attempt at a solution

    I thought that the tension in the left rope was larger, but this turned out to be wrong. I thought it must be, because omega was positive and constantly increasing, meaning the pulley was rotating counter clockwise. Also, just from the angular velocity/acceleration, I'm not sure how to relate T_L to T_R.

    Please, I could really use some help!
  2. jcsd
  3. Nov 14, 2007 #2
    is it possible for you to have the diagram? I, personally, like to have a strong grasp on understanding the problem. By the way, your equation isn't correct for torque. Torque is basically the cross product of a Force vector and the Radius (displacement vector).

    P.S. you dont HAVE to show a diagram. But I don't really understand the problem. sorry :(
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