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Three Pulleys 3 masses, find tension

  1. Dec 9, 2012 #1
    1. The problem statement, all variables and given/known data

    Three objects mI. m2 and m3 are suspended
    from three massless and frictionless pulleys as
    shown in the diagram. ml is 6 kg, m2 is 2 kg
    and m3 is 3 kg. Find the tension of the string
    when the system is set in motion (i.e. all
    masses are moving). Answer in N

    Options are:
    (a) 11.3 (b) 12.1 (c) 13.5 (d) 14.2

    ..O....O...... Top 2 pulleys attached to ceiling, m1 hangs from 1st pulley, m2 is attached
    .| |..| |..... to the middle pulley, m3 hangs from third pulley.
    [] m2 []

    2. Relevant equations

    3. The attempt at a solution

    I made 3 equations, tried to relate them but I am getting 15.68N instead of any of the options (this was an old exam question). It's too far from 14.2 to be right. Here were the four equations I made:



    I keep getting none of the possible answers but I think I'm doing it right. Where did I go wrong?
  2. jcsd
  3. Dec 9, 2012 #2


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    Gold Member

    Your equations are right but your answer is wrong. Please post your working.
  4. Dec 9, 2012 #3

    From 4th eqn:




  5. Dec 9, 2012 #4


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    Science Advisor
    Homework Helper
    Gold Member

    Oh, sorry, I misread the end of your first post. I thought you were getting 14.2. So, I agree with you, it's something around 16.
  6. Dec 9, 2012 #5
    k thanks
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