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Moment about a rigid bar

  1. Oct 5, 2013 #1
    1. The problem statement, all variables and given/known data

    Please refer to the image.

    2. Relevant equations

    Sum of clockwise moment=sum of anticlockwise moment

    3. The attempt at a solution

    I had drawn out the force diagram and listed out the information required.

    The question asks me to find force acting by the support B.

    I troubled myself by taking moments about A and multiplying every forces with their respective distances from A.

    However the answer was simple, they just added all other forces together, 33 + 4.4 + 129 = 166N.

    I can't figure out where is the pivot. Or is there even a pivot? What's the theory behind this calculation?

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    Last edited: Oct 5, 2013
  2. jcsd
  3. Oct 5, 2013 #2


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    But how was the 129N figure obtained? You'd need to take moments to derive that.
  4. Oct 5, 2013 #3
    Haruspex, the 129N is obtained from another part of the question which is correct.
  5. Oct 5, 2013 #4


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    Then it is indeed simple to determine the force at B in the way they use. For the system to be static, the sum of the vertical forces must be 0. You could also deduce it by taking moments about anywhere along the line except B.
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