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Homework Help: Tensions equilibrium

  1. Apr 27, 2014 #1
    1. The problem statement, all variables and given/known data
    see pic

    2. Relevant equations

    3. The attempt at a solution
    Ive worked out T1 which is T1=F1(-4i-5j-10k/11.8743) = T1(-0.337i-0.421j-0.842k)
    and T2=F2(-4i-5j-10k/11.8743) =T2(0.337i-0.421j-0.842k)
    and the next step is to find the unit vector of force M = 20kn but how do i work out unit vectors from the diagram if the lengths aren't given?

    (the answer given is 6.84i + 18.794j for the unit vector of M=20kN but how??)

    Attached Files:

    Last edited: Apr 27, 2014
  2. jcsd
  3. Apr 27, 2014 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    You obviously don't realize that a 'unit vector' has a magnitude = 1, which is why it's called a unit vector.

    You know the magnitude of the force M (which = 20 kN) and you are shown the direction of the M vector in the diagram. The M-vector is parallel to the x-y plane and it makes an angle of 20 degrees with the positive y-axis. Ergo, you can work out the components of M using simple trigonometry.
  4. Apr 28, 2014 #3
    oh i get it now thanks
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