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Homework Help: Magnitude of moment about axis (Space Truss)

  1. Aug 27, 2012 #1
    1. The problem statement, all variables and given/known data

    Determine the magnitude of the moment of the force F about the axis CA of the tripod
    ABCD, if F = {40i -30j -100k}N.

    Image attached.

    2. The attempt at a solution

    Based on a similar question I found in the textbook my method to solve this question:

    Find UCA = rCA/rCA = (-2/√8)i + (2/√8)j

    Find MCA = UCA.(rDC?? * F)

    However, I am unsure if the finding the position vector rDC is correct?

    Am I going about this the right way?

    Please help.



    Attached Files:

  2. jcsd
  3. Aug 28, 2012 #2


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    Staff Emeritus
    Science Advisor
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    Gold Member

    Here's your image:


    First of all your rCA must be incorrect. Look closely. Point A is 1.5 m from the origin on the y-axis. Point C is 2 M from the origin on the x-axis.
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