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Math Help - Moments

  1. #1
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    Moments

    A uniform rod AB of length 5m and mass 6kg is pivoted at C where AC =1.5m. Calculate the mass of the particle which must be attached at A to maintain equilibrium with the rod horizontal.

    help i cant get right answers for these questions. The answer is 4kg
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  2. #2
    Senior Member Twig's Avatar
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    You need the total torque to be zero.

    \sum \tau = 0

     0 = mg(1.5)-M_{rod}g(1) \, \Rightarrow m = 4 kg
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  3. #3
    Junior Member mathmonster's Avatar
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    Quote Originally Posted by Sundae View Post
    A uniform rod AB of length 5m and mass 6kg is pivoted at C where AC =1.5m. Calculate the mass of the particle which must be attached at A to maintain equilibrium with the rod horizontal.
    help i cant get right answers for these questions. The answer is 4kg
    Take clockwise moments and anti-clockwise moments (either side of the pivot)
    so you have clockwise moment = 6kg x 1m(because mass acts through middle of the beam, because it is uniform and this is 1m from the pivot)

    and mass at A = M, therefore counter-clockwise moment = 1.5m x Mkg

    moment must be equal to maintain equilibrium, and so

    6x1 = 1.5M ==> 6/1.5 = M = 4kg.
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