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Homework Help: Statics problem

  1. May 16, 2008 #1
    Hello everyone

    Iam practicing for my exam in mechanics and I cant figure out how to solve this problem. I need to find the forces in B and C.

    Please help..

    Greetings from cold norway

  2. jcsd
  3. May 16, 2008 #2

    This is how I think the forces is working. Cant figure out if this is correct
  4. May 16, 2008 #3
    the reactions at the supports look correct. you need to isolate the top portion of the structure (sum moments about C) to start getting answers.
  5. May 16, 2008 #4


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    When you attempt to solve the external reaction forces, you have 4 unknowns at those supports, but only the 3 equilibrium equations (sum of forces in x direction = 0, sum of forces in y direction = 0, and sum of moments about any point = 0). Thus, you'll need another equation to solve for all the support reactions. As haynewp has noted, you've got to start disassembling the frame with free body diagrams of the members in order to get the 4th equation you need, taking advantage in identifying the '2 force' members that will take axial load only.
  6. May 17, 2008 #5
    I went ahead and solved it. There is actually one other step I used prior to summing moments about point C. You still have to isolate part of the structure as noted above which is the most important idea for this problem. I also found your vertical reaction at D looks like it is going in the wrong direction (should be pointing down). But I only knew this for sure after I went through the rest of the required process.
  7. May 17, 2008 #6


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    Welcome to PF!

    Hi eivert! Welcome to PF from warm but rainy England! :smile:

    I'm sorry, but your diagram will not help.

    (For example, on your diagram at B, there should be the force of BE on AC and the equal and opposite force of AC on BE)

    You need separate diagrams for each of the rods.

    Start with rods CG and BE (as PhanthomJay suggests). :smile:
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