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Finding Tension on cables

  1. Mar 27, 2009 #1
    1. The problem statement, all variables and given/known data

    pysicssign.jpg



    Obviously the picture is not to scale

    3. The attempt at a solution
    I really have no ides where to start I assume you have to use moments to find the tension in each cable but im really not sure how to go at it.
    I think the 20 N force hanging from the sign would only act through the one cable and wouldnt effect the other cable because it is the same distance from the end as the support cable.

    Thanks for the help
     
  2. jcsd
  3. Mar 27, 2009 #2

    djeitnstine

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    Start off by drawing your free body diagram. Since the material has a constant density its CG will act at the center of the sign. Next, you find the sum of the forces in the y direction. Also you are correct in saying that you can sum the moments. Just one pointer, try finding the point with most forces acting at it.
     
  4. Mar 27, 2009 #3
    I really still dont know where to start can someone go over the steps in doing this question
    Thanks
     
  5. Mar 27, 2009 #4
    Break the figure apart and treat each body as a separate FBD. Show the forces acting on that body and then start writing your equations.
     
  6. Mar 27, 2009 #5

    djeitnstine

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    Hmm that is too much work, he can do this using 2 equations by treating the whole thing as one object and analyze the tension in the cables alone.
    It seems he wants us to do it for him but if he could just separate the body from the wall, then sum the forces in the y direction, and sum the moments (or torques) about either the point where Ta or Tb is acting then he is done.
     
    Last edited: Mar 27, 2009
  7. Mar 27, 2009 #6
    A little bit of discovery is a wonderful learning experience.
     
  8. Mar 27, 2009 #7

    djeitnstine

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    Haha, i'll place it as a spoiler then ;)
     
  9. Mar 28, 2009 #8

    PhanthomJay

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    The problem statement is incorrect, based on the dimensions shown. One of the rods will not be in tension.
     
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