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Statics- Resultant couple moment

  1. Jun 8, 2013 #1
    1. The problem statement, all variables and given/known data
    If F_1 = 100N , F_2 = 120N and F_3 = 80N , determine the magnitude and coordinate direction angles of the resultant couple moment.

    2. Relevant equations
    M=r x F
    MR=Ʃ(r x F)

    3. The attempt at a solution
    I found the couple moment for each force:
    M1=F1d=100(0.2) or (-20j using right hand rule)
    M2=F2d=120(0.2) or +24i
    M3=F3d=80(0.2) or -16k
    M4=this is what im having problems with...not sure how to get the moment for F4... if do 150(.3)(cos30)=38.97 i get the wrong resultant.

    The correct answer should be (MC)R=71.9 Nm...
    Any help would be greatly appreciated.

    Attached Files:

  2. jcsd
  3. Jun 8, 2013 #2


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    hi rico22! :smile:
    i don't get 71.9 unless i use .33 instead of .3 :redface:
  4. Jun 8, 2013 #3


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    Note that the F4 couple is not in the x-direction. It is parallel to the xy plane but it has both x and y components which you will need to work out.
  5. Jun 9, 2013 #4


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    ooh, i didn't notice that! :redface:

    i read the axis of that pipe, and the short line above the positive x-axis, as one continuous straight line! :rolleyes:

    yes, now i get 71.9 … thanks, Tsny :smile:
  6. Jun 11, 2013 #5
    thanks for the replies guys...
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