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Homework Help: Tension in cable and reaction force

  1. Oct 20, 2013 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
    For this problem, what I am confused about is the fact that the Z direction parts of the tension will tend to rotate in a direction different from the Y components of the tension and the 850 lb vertical force. I am not sure how to reconcile the moments involving the Z-component into my moment equation around point A, which I know should be zero. The x component is along the line of point A, so there moments must be zero.

    I remember solving 2-D moments and the x components and y components will cause rotation in the same direction, but with 3-D moments it appears the z component will rotate around a different direction than the y component will, so it seems unlikely that they can be added together like the x and y components can be in 2-D torques.

    I know the page is cut off, but I don't get the right value when I do it this way. I know the part about the forces is correct, there is something that I am missing though with respect to taking a moment around point A, which I want to do in order to get rid of the reaction forces at A.

    Attached Files:

  2. jcsd
  3. Oct 20, 2013 #2
    Taking a moment with respect to point B should give you more simple equations.

    If you are doing scalar analysis, you should break your moment into Mx, My, Mz. Use M = r x F instead for vector analysis.
  4. Oct 20, 2013 #3
    Thanks, I took the moment at point B and got it solved
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