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Homework Help: Determine the Forces in the Specified Members.

  1. Oct 21, 2012 #1
    1. The problem statement, all variables and given/known data
    Determine the forces in members BC, CF, and EF of the loaded truss. Forces are positive if in tension, negative if in compression.

    I have included an image

    2. Relevant equations
    ƩM = 0
    ƩFy = 0
    ƩFx = 0

    3. The attempt at a solution
    I'm a little stuck on this one.

    I tried using method of sections, whereby I drew a line through the middle of lines BC, CF and EF and then focused on everything to the right of that line. What this gave me is a system with two L forces, one at E and another at D as well as the forces of the members BC, EF and CD.

    From here I tried to take the moment about point C,

    ƩMC = 0

    0 = -L(d) + EFcos(17)

    however I ran into difficulty because I couldn't figure out what the distance of CE is.

    Help would be appreciated

    Attached Files:

  2. jcsd
  3. Oct 22, 2012 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    It's just a bit of trig and geometry to find the distance CE. The length 'd' is known and a couple of the angles....find the vertical legs of triangles with side d and angle theta...draw a sketch....otherwise, your equation is good when you add your omission noted in red
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