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Homework Help: Solid mechanics problem (pretty much a static problem)

  1. Feb 1, 2009 #1
    1. The problem statement, all variables and given/known data
    A pin-jointed truss ACE is part of a cable-hoist system that is used to lift cargo boxes, as shown in Fig P1.4-5. The cable from the lift motor to the cargo sling passes over a 6-in pulley that is supported by a frictionless pin at C. The weight of the cargo box being lifted is 1500 b. Neglecting the weight of the cables, determine the reactions at the pin supports at A and E, and determine the axial force in each of the following members: F1 (in member AB), F2(in member AD), and F3 (in member DE). Explain the answer you got for the value of F2.

    2. Relevant equations
    Pretty much all the basic statics equilibrium equations. (Sum of F_x=0, F_y=0, M_z=0)

    3. The attempt at a solution
    I drew up a picture, but the main problem I'm having is how to deal with the sum of the moments. It's been a while since I've done any statics problems, so I'm unsure of how to incorporate the moment that the tension in the cable causes. I think I can find out everything else the question asks once I get past this small hurdle.

    Attached Files:

    Last edited: Feb 1, 2009
  2. jcsd
  3. Feb 2, 2009 #2


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    Homework Helper

    DyslexicHobo: Preferably reverse the direction of reaction force Ft in your diagram, if you wish. You know the magnitude of Ft is equal to the cable tension, right? And you know the direction of Ft. Resolve Ft into components Ftx and Fty. You know reaction force Fe is collinear with member DE, right? Resolve Fe into components Fex and Fey. Now sum moments about any point you wish.
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