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Homework Help: Force and moment couple

  1. Oct 21, 2008 #1
    1. The problem statement, all variables and given/known data
    A 63lb force F and 560lb in couple M are applied to corner A of the block shown. Replace the given force-couple system with an equivalent force-couple system at corner D

    2. Relevant equations

    3. The attempt at a solution
    I actually solved the problem but I had to guess and check. I am not sure why it works the way it worked so I was hoping somebody could explain this to me.

    First i found the components of M. then I found the components of the Moment created by F by doing A X F. I called this M1
    Then I put the same force at point D and did D X F giving me M2

    in order to find the answer I had to do M - M1 + M2. Can someone explain why I had to do M - M1 + M2?
  2. jcsd
  3. Oct 21, 2008 #2
    Can you show the diagram?

    The total torque (and total force) should be the same in both cases.
  4. Oct 21, 2008 #3
    I dont have a way of getting a good picture of it. but i can give u this info if it helps:
    A (0,7.2,4.8)
    D (14.4,0,0)
    F = <54,27.1,-18>
    M (@ point A) = <448,-336,0>
    M1 = AXF = <-259.7,259.2,-388.8>
    M2 = DXF = <0,259,390.24>
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