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Hanging Mass - Answer says that I am wrong

  1. Jun 25, 2008 #1
    1. The problem statement, all variables and given/known data
    The relevant forces are tension in the rope, which acts in two directions on the object, and the force of gravity, the object's weight which acts down.

    Calculate the tension in the rope.

    mass= 2.0 kg
    tension force = unknown

    2. Relevant equations

    Force (tension) - Force (weight of mass) = 0 (because the system is in equilibrium).

    3. The attempt at a solution

    I put it up on image-shack:


    I got 38 Newtons of tension on each rope. But the text tells me that I am wrong and that EACH string should equal 76 Newtons.
  2. jcsd
  3. Jun 25, 2008 #2


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    Given your angle of 15, 38N should be correct....but the only way to get their answer is if the angle is approximately halved.
  4. Jun 25, 2008 #3


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    Looks like a typo possibly born out of someone carelessly adding where they shouldn't. Using half the angle only yields 75N for me whereas the problem in the illustration yields something quite close to 38N (37.9N for me). For the text calculation to be based on just half the angle then the claim 76N would be too much in error. To claim exactly twice then suggests carelessness in preparing the text description of the answer.
    Last edited: Jun 25, 2008
  5. Jun 25, 2008 #4
    your right,.. all they did was take 19.6/sin(15). should have been 19.6/(2sin(15))
  6. Mar 20, 2011 #5

    am i right?
    Last edited: Mar 20, 2011
  7. Mar 20, 2011 #6
    19.6/2sin15 is coming something 15.07!
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