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Homework Help: Help with tension

  1. Dec 16, 2007 #1
    1. A lamp with mass 42.6 is hanging vertically from wires. Wire with T1 is pulling straight up on the lamp, and then it branches off to other wires with T2 and T3. T2 forms an angle of 120 degrees with the horizontal (or 60 degrees facing left). T3 forms a 30 degree angle with the horizontal. Find the Tensions

    2. Sum of Forces = 0

    3. T1 is just the force of gravity on the lamp so (42.6 * 9.81) = 418 N. Then I broke T2 and T3 into x and y components. T2x = T2cos60, T2y = T2sin60. T3x = T3cos30, T3y = T3sin30. Then I built my equations. (-T2cos60) + (T3cos30) = 0. And (-418) + (T2sin60) + (T3sin30) = 0. But then I get stuck

    Then also if you could explain this one real quick
    http://img180.imageshack.us/img180/1196/tensiololnxe9.jpg [Broken]

    I don't know if any real work is needed, I don't know, tension just doesn't make much sense to me, so if someone could explain it I would be really thankful.
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Dec 16, 2007 #2
    If you set up the equations correctly you can use simultaneous equations to find one of the tension forces.

    As to the second questions I believe it's "c".

    The reasoning is that the tension in the rope at C needs to be greater than all three of the boxes friction forces
  4. Dec 17, 2007 #3
    I still really don't get what to do
  5. Dec 17, 2007 #4


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    What are the relative positions of T1, T2 and T3? Are they in the vertical plane? In your attempted solution there is no T1.
  6. Dec 17, 2007 #5


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    Homework Helper

    If you think T1=mg, you are wrong. The sum of ALL of the vertical components of the tension is equal to mg. And the sum of all of the horizontal components is equal to zero.
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