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Homework Help: Truss - Method of Joints in terms of load P

  1. Oct 21, 2012 #1
    Hello guys. I would like someone to check that I am doing this problem correctly. The answer given in the book is 0.577(P) for FAB and FAE which differs from the answer I get.

    1. The problem statement, all variables and given/known data
    Determine the force in each member of the truss in terms of the load P and state if the members are in tension or compression.
    Drawing with work http://imagebin.org/232748 [Broken]

    2. Relevant equations

    [itex]\Sigma[/itex]MA = 0
    [itex]\Sigma[/itex]Fx = 0
    [itex]\Sigma[/itex]Fy = 0

    3. The attempt at a solution
    Entire truss system

    [itex]\Sigma[/itex]MA = 0
    -L(P) + 2(L)(Dy) = 0
    Dy = [itex]\frac{P}{2}[/itex]

    [itex]\Sigma[/itex]Fx = 0
    Ax = 0

    [itex]\Sigma[/itex]Fy = 0
    Ay - P + Dy = 0
    Ay = [itex]\frac{P}{2}[/itex]

    Forces at pin A

    [itex]\Sigma[/itex]Fy = 0
    Ay - [itex]\frac{1}{\sqrt{2}}[/itex](FAB) = 0
    FAB = [itex]\frac{\sqrt{2}}{2}[/itex](P)

    [itex]\Sigma[/itex]Fx = 0
    -[itex]\frac{1}{\sqrt{2}}[/itex](FAB) - FAE = 0
    FAE = [itex]\frac{-P}{2}[/itex]
    Last edited by a moderator: May 6, 2017
  2. jcsd
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