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Heres a tough sign question with equilibrium that will be on the test.

  1. Apr 29, 2009 #1
    1. The problem statement, all variables and given/known data
    A sign that weighs 168N is supported by 2 ropes, a and b, that make 22.5 degree angles with the horizontal. The sign is not moving, what forces do the ropes exert on the sign. I have 45 minutes to figure this out.


    2. Relevant equations
    I dont know any equations



    3. The attempt at a solution
    I dont no where to start
     
  2. jcsd
  3. Apr 29, 2009 #2

    dx

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    Let the tension in the ropes have magnitude T. What is the expression for the vertical component of the tension in each rope? What is the total vertical force on the sign due to the ropes in terms of T? What value must this force have to balance the weight of the sign?
     
  4. Apr 29, 2009 #3
    ok I dont understand that can you show me the first step through the numbers.
     
  5. Apr 29, 2009 #4

    dx

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    Which part don't you understand?
     
  6. Apr 29, 2009 #5
    I dont know Im bad with this kind of stuff
     
  7. Apr 29, 2009 #6

    dx

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    Do you know what tension is? Which direction is it pointing in? Do you know how to use the trigonometric functions to find the components of vectors?

    For example, if a vector is pointing in a direction 10 degrees above the horizontal, and has magnitude 50, it has a horizontal component 50cos(10). Are you familiar with this sort of thing?
     
  8. Apr 29, 2009 #7

    Andrew Mason

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    By symmetry you can see that there should be no difference between the magnitude of the tension force in each of the two ropes.

    What is the downward force? Does the sign accelerate? So what can you tell about the net vertical force (downward - upward)? So what is the sum of the upward components of tension in the ropes? What does that tell you about the magnitude of the tensions in the ropes? What is the net horizontal force on the sign? (ie. does it accelerate sideways?). What are the horizontal components of the tension forces?

    AM
     
  9. Apr 29, 2009 #8
    ok I have to go Im going to try and ask my teacher about this question before I write it.
     
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