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A problem in sections method in analyzing structure

  1. Apr 12, 2014 #1
    1. The problem statement, all variables and given/known data

    Determine the force in members BF, BG, and AB, and state if the members are in tension or
    compression.


    2. Relevant equations

    Method of sections

    3. The attempt at a solution

    Now I cut the sections FB, BG and BA... I took the lower end. I now have three unknowns. I set all required force in all three members in TENSION so if I get any negative number, it is compression.

    I set up three equations

    Fx = 0 ; FB + 25 + GB cos 45 = 0
    Fy= 0 ; AB + 50 - 45 + GB sin 45 = 0
    Mg= 0 ; 4AB - 45*4 - FB*4 = 0

    After arranging it and typing it to solve the three simultaneous equations, I get math error.. Where is my MISTAKE?? clarify please and I would be so thankful. The thumbnail is attached.

    Thanks!
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     

    Attached Files:

  2. jcsd
  3. Apr 12, 2014 #2

    nvn

    User Avatar
    Science Advisor
    Homework Helper

    ehabmozart: When you cut a section, you must cut through the entire structure. Therefore, e.g., you need to perhaps extend your cut, to cut through member EF, also. Or change your cut, to cut through member FG.
     
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