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Simple problem on tension and force

  1. Aug 30, 2008 #1
    1. The problem statement, all variables and given/known data
    Ropes 3m and 5m in length are fastened to an object that is suspended over a cieling. the object has a mass of 5kg. the ropes, fastened at different heights, make angles of 52 degree and 40 degree with the horizontal. Find the tension in each wire, and the magnitude of each tention.


    2. Relevant equations



    3. The attempt at a solution
    I kno that the tension on one rope, A and the tension on the other rope, B equal to the mass times gravity.
    so AT+BT = mg
    and i want to find the a equation for AT and BT

    Just wondering, since i kno the angle and length of the rope, i know the verticle component of the rope. But then i don't kno where to go after that
     
  2. jcsd
  3. Aug 31, 2008 #2
    What you need to do is draw a force diagram and write down all the horizontal and vertical components of tension as a result of the mass.

    Next, you need to use Newton's second Law and find the net force in both horizontal and vertical directions.

    Just remember that net force (vector sum of components) = ma, and if the object is not moving, then the net force is zero.
     
  4. Aug 31, 2008 #3

    tiny-tim

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    Hi k1point618! :smile:
    No, that's wrong … that only works if both ropes are vertical.

    As jaseh86 says, you must treat the horizontal and vertical components separately.

    The vertical ones will add to mg, and the horizontal ones to … ? :smile:
     
  5. Aug 31, 2008 #4
    Horizontal adds to Zero!

    Well, then i have
    ATsin52 + BTsin40 = mg, and also


    ATcos52 + BTcos40 = 0 ?
     
  6. Aug 31, 2008 #5

    tiny-tim

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    Yes! :smile:
     
  7. Aug 31, 2008 #6
    So i was wondering, why does the problem give the length of the ropes? and how does the high difference of the cieling affects the problem?
     
  8. Aug 31, 2008 #7

    tiny-tim

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    hmm … it's a weird question, because you suspend things under a ceiling, not over it. :confused:

    Are you sure you have given us the full correct question?
     
  9. Aug 31, 2008 #8
    Sorry, Over a ceiling, but the ropes are fastened at different heights.
     
  10. Aug 31, 2008 #9

    tiny-tim

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    Then I've no idea why they give you that information. :redface:
     
  11. Aug 31, 2008 #10
    so the different hieghts of the ceiling does not matter to the problem?
     
  12. Aug 31, 2008 #11

    tiny-tim

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    No!!
     
  13. Aug 31, 2008 #12
    K, THANK YOU!!:smile:
     
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