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Homework Help: Basic torque problem

  1. Nov 20, 2012 #1
    1. The problem statement, all variables and given/known data

    a hoop of mass m and radius r has a cord wrapped around it the hoop is released while holding the string the hoop rolls without slippage
    write out force and torque eqns on the hoop
    given m, r determine downward accel

    2. Relevant equations

    Torque = I alpha
    Torque = r x F

    3. The attempt at a solution

    Torque = I * alpha
    I of hoop = m*r^2
    alpha = r*a

    r x F = m*r^3 * a

    this F must have relationship to gravity and tension right? if it were ma then my as cancel

    Fy should be ma = Tension - mg ?

    im lost at this point, thanks for any help
  2. jcsd
  3. Nov 20, 2012 #2


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    Draw a free body diagram for the hoop.

    Torque is calculated about some reference point. What point are you choosing?

    The following link includes the excerpt below: https://www.physicsforums.com/showthread.php?t=414380

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