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Please help with Static problem

  1. Apr 11, 2006 #1
    I need Help with a Equilibrium in Three Dimension problem I am having trouble with finding the moment about A formula, I get a little confused with it. I have found sum of the fores in x,y,z=0, for X. Ax+Tdf-.385Tcg=0
    for Y. Ay-.923Tcg=1800, and for Z. Az-Tde=0 I am tring to take the moment about a. So far I have got Ma=0; (8i=12k X -1800j) I do not know what to put down for the tensions in the other cables

  2. jcsd
  3. Apr 11, 2006 #2


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    Staff: Mentor

    Look in each of the planes (x-y), (y-z) and (x-z).

    The tensions put a force on the structure in the direction of the wire/cable.

    So DE applies a force from D toward E, and DF applies a force on the structure pointing from D to F.

    CG has points from C to G, but needs to be resolved into two components, one down and the other pointing parallel with DF.

    The downward force component of CG also pulls down on A, in addition to the 1800 lbs at x.
  4. Apr 11, 2006 #3
    This is a very complex problem. For CG, it will have a force in ALL 3 directions. I don't have the time, but you are to have several equations to work out.
  5. Apr 13, 2006 #4
    Astronuc is right. Break the forces apart into components, then solve for equilibrium in each of the 3 planes. This is a determinate problem.
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