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Statics: Finding the moment on point B?

  1. Sep 25, 2016 #1
    1. The problem statement, all variables and given/known data
    fTJnj42.jpg

    Determine the moment about point B of each of the three forces acting on the beam.


    2. Relevant equations
    M = F*d⊥

    3. The attempt at a solution
    I went and found the components for each of the forces. Please double check it if I did them right:

    F1 :
    Fx = 0
    Fy = 375 lb

    F2:

    Fx = -500(3/5)lb = -300lb
    Fy = -500(4/5)lb = -400lb

    F3:
    Fx = 160cos30° = 138.6lb
    Fy = -160sin30° = -80lb

    If those components are right, I'm having trouble finding their perpendicular distances.
     
  2. jcsd
  3. Sep 25, 2016 #2
    Based on the figure above is the
    F*d⊥ for each of the forces are (without the sign convention/right hand method applied):
    F1
    Fx1 = 0
    Fy1 = 375lb*19ft

    F2
    Fx2 = -300lb(0.5ft)
    Fy2 = -400lb(19ft)

    F3
    Fx3 = 138.6lb(0.5ft)
    Fx3 = -80lb(19ft)

    I got 19ft by adding the three dimensions below the beam. Is that correct?
     
  4. Sep 25, 2016 #3

    David Lewis

    User Avatar
    Gold Member

    Label forces with F, and moments (force times distance) with M.
    To calculate the moment of force F1 about point B, how far is F1 from point B?
     
  5. Sep 25, 2016 #4
    Ahh! 11 ft!
     
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