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Forces in truss

  1. Jul 3, 2016 #1
    1. The problem statement, all variables and given/known data
    i dont understand the 8/BD = x/EB
    Can anyone explain about it? There's no point E in the diagram....

    2. Relevant equations


    3. The attempt at a solution
     

    Attached Files:

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    • 271.jpg
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  2. jcsd
  3. Jul 3, 2016 #2

    billy_joule

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    I can't see that in your attached images? Is there an image missing?
     
  4. Jul 3, 2016 #3
    in post#1
     
  5. Jul 3, 2016 #4
     

    Attached Files:

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    • 271.jpg
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  6. Jul 3, 2016 #5

    billy_joule

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    Yeah, I see the two images in your OP and then again in post #4.

    But I don't see this term:
     
  7. Jul 3, 2016 #6
    here
     

    Attached Files:

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    • 272.jpg
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  8. Jul 3, 2016 #7

    billy_joule

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    Ok.
    We still don't have the full problem statement as the dimensions of the structure don't appear in any of your three images.
    I'm guessing the calc is some geometry to find some unknown length. Maybe E is a typo. Hard to say really, that's why PF homework rules state that you must include the entire question :wink:
     
  9. Jul 3, 2016 #8
    in second image of post #6
     
  10. Jul 3, 2016 #9

    billy_joule

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    I see no dimensions (or angles) on either image in post #6. The second image appears to be part of the worked solution, how could you be expected to solve the problem if the geometry of the truss isn't given?
     
  11. Jul 3, 2016 #10

    NascentOxygen

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    Staff: Mentor

    We need you to post the complete figure and data for the problem as given. There are no dimensions marked on what you have provided.
     
  12. Jul 4, 2016 #11
    the full exact question is in photo 271....That's the complete question.....
    why it's /BD = x/EB???
     
  13. Jul 4, 2016 #12

    billy_joule

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    Well, then the question is incomplete and unsolvable.
     
  14. Jul 4, 2016 #13
    You don't need dimensions in a statically determinate frame - just the proportions. Guessing that the left hand triangle is in a 3/4/5/ proportion, the figures 6 and 8 make sense. The choices of forces as multiples of 14 suggest the question is looking for an answer that can be achieved without a calculator. The suggested reactions are wrong in my opinion and this reinforces the notion that it is useless to look for internal forces if the external reactions are incorrect. The external reactions should have been checked, for example by taking moments about any point not already used to obtain tham.
     
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