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Homework Help: The bar is in static equilibrium W = 15N, Na = 11N

  1. Sep 24, 2010 #1
    1. The problem statement, all variables and given/known data
    The bar is in static equilibrium W = 15N, Na = 11N and Nb which is perpendicular to the bar,Nb = 5.66N.What is the magnitude of tension forceT?

    2. Relevant equations



    3. The attempt at a solution
    W - Na - Nb*sin(theta) = 0;
    15 - 11 - 5.66*sin(theta) = 0
    theta = 45 deg
    Nb*cos(theta) = T
    T = 5.66*cos(45)
    T = 4 N
    But the options given are a)17.79N b)25N c)12N d)21N e)0.9 m^2
    solve this problem,,,,,,,,,,,,,
     

    Attached Files:

  2. jcsd
  3. Sep 24, 2010 #2

    PhanthomJay

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    Re: statics

    I get your answer also.
     
  4. Sep 25, 2010 #3
    Re: statics

    This is not a well-defined problem because distances have not been given. You have used the law of equilibrium for equating forces in two directions, but you have not used the principle of sum of moments is zero. Wht happens if you try to check your answer wiith T=4? That you cannot do without distances (or at least the ratio of the distances on the rod)
     
  5. Sep 25, 2010 #4

    PhanthomJay

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    Re: statics

    The bar is at a 45 degree angle. Although the distances are not given, W must be located a certain fraction of the bar length from one end, about half way up ,based on the values given.
     
  6. Sep 27, 2010 #5
    Re: statics

    I would encourage indiangeek to check statics problems using all the equations of equilibrium available. You might be able to determine the exact location of Nb (in relation to W and Na by using the principle of moments. Having done that, the alleged solution T=4 can be checked.
     
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