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Moment about a point

  1. Oct 15, 2015 #1
    1. The problem statement, all variables and given/known data
    for M2 , if i take the moment at pont C , then my ans would be (0.3i) x ((125X(3/5) j +125(4/5) k )= 30j +22.5k
    Which is not same with the book which use moment about D . why ? Is the value at the triangle at te upper part incorrect (circle part) ?

    2. Relevant equations


    3. The attempt at a solution
     

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  2. jcsd
  3. Oct 15, 2015 #2
    Picture is too small to read.
     
  4. Oct 15, 2015 #3
     

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  5. Oct 15, 2015 #4
    Still too small. Just blow up the diagram.
     
  6. Oct 16, 2015 #5

    haruspex

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    If you are taking moments about C then presumably you are considering the force at D. Isn't that in the direction -3/5j+4/5k? And should't the displacement vector be -3i?
     
  7. Oct 16, 2015 #6
    Ya, I would ended up getting 22.5k +30j . But if I take moment about D , I would get 22.5j+30k... Is it correct???
     
  8. Oct 16, 2015 #7

    haruspex

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    No, sorry, I had it wrong. The force at D is in the direction -4/5j+3/5k.
     
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