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Homework Help: Rotational Motion

  1. Jan 22, 2005 #1
    I have a diagram for this at http://snipurl.com/diagr [Broken]

    There is a uniform disk with radius R, mass M, it has a string wrapped around it and is attached to a fixed rod.
    Part 1: Show the tension in the string is 1/3 the weight of the disk

    what i have done for this is

    [tex] Torque=Fd [/tex]
    and setting the force equal to Tension
    [tex] Torque=TR [/tex]
    then [tex] \sum Torque=I\frac{a}{R}[/tex] and i used [tex]I=\frac{1}{2}MR^2[/tex]for the moment of inertia

    Then [tex] TR=\frac{1}{2}MRa[/tex]
    and then acceleration is just g, so i get the tension equals 1/2 the weight. where have i gone wrong????
    Last edited by a moderator: May 1, 2017
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  3. Jan 22, 2005 #2


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  4. Jan 22, 2005 #3
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