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Homework Help: Moment of a Couple, need help making sure answer is reasonable

  1. May 22, 2013 #1
    1. The problem statement, all variables and given/known data
    Given the following structure, determine the value of F such that the resultant couple moment on the structure is 200 pound-feet clockwise.
    I'm not looking for help here per se, just if this is a valid method of solution:
    Because the moment of a couple is a free vector, it seems to me that the moments of the two couples can be placed at point B without any problem.
    Then it would also make sense to me that: [itex]M_{\text{couple with F}}=F\cdot 2\sqrt{2}[/itex] pound-feet clockwise, and [itex]M_{\text{150 lb couple}}=600\sqrt{2}[/itex] pound-feet counterclockwise, which gives me that [itex]F\cdot 2\sqrt{2}-600\sqrt{2}=-200[/itex], which implies that [itex]F=229 \text{ lb}[/itex].
    Is this a valid method of solution? It makes sense to me, but I'm not sure if it makes sense to anyone else.
    Last edited: May 22, 2013
  2. jcsd
  3. May 23, 2013 #2


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    I'm very rusty on this but seems to me that you would need to know force at A to use your method. Perhaps I'm wrong.
  4. May 23, 2013 #3
    look again at your root 2. It's not quite right. You can check your answer by taking moments about any point.
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