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Finding tension? please help

  1. Jan 15, 2009 #1
    My teacher is a dumbass and a horrible teacher. I swear he never taught us how to find tension and the "textbook" gives us long stories about little Billy and Bobby but never explains how to DO the problems. I need help for this question. Please explain if you can

    1. The problem statement, all variables and given/known data

    A street lamp weighs 150N. Its supported by two wires that form an angle of 120 degrees with each other. The tension in the wires are equal.
    a) what is the tension in each wire supporting the street lamp?
    b) If the angle between the wires is reduced to 90 degrees, what is the tension in each wire?

    2. Formulas Needed

    no clue. sorry

    3. Attempts
    I don't know any of this so I couldn't even attempt to do it. I don't know where to even start
  2. jcsd
  3. Jan 15, 2009 #2


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    Draw the free body diagram with all the forces acting. Then split then tensions in the wires into x and y components. Then use the fact that for equilibrium, the sum of the forces in a specified direction is zero.
  4. Jan 15, 2009 #3


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    Welcome to PF.

    Maybe you shouldn't be so hard on your teacher? At least the teacher likely knows how to figure the problem?

    But as to equations this is a matter of resolving the force vectors from the information given. Drawing a diagram should be helpful.

    You know what the vertical components of the tension must be in the two lines, hence you should be able to figure the Tension itself.
  5. Jan 15, 2009 #4
    this doesnt help at all.
  6. Jan 15, 2009 #5


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  7. Jan 15, 2009 #6
    'kay, i figured it out on my own already. bye :)
  8. Jan 15, 2009 #7


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    That's great. The system works and you learned how to solve the problem.

    If someone had told you the answer you might have difficulty come exam time.
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