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Homework Help: 3 mass, 3 pulley

  1. Sep 8, 2012 #1


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    1. The problem statement, all variables and given/known data
    I I I = string
    O O O = massless frictionless pulley
    I II I
    ' O " . = mass 1
    : : = mass 2
    " = mass 3

    Find acceleration of each mass.

    2. Relevant equations
    conservation of String
    3. The attempt at a solution
    Tension is same
    T-m1g = m1a1
    2T-m2g = m2a2
    T-m3g = m3a3

    a1=a3=1/2a2 <- im not sure how to use conservation of string... shouldn't a1 is equal to a3 because there are connected to same sting..
    so my question is how to get relationship between/among accelerations

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    Last edited: Sep 8, 2012
  2. jcsd
  3. Sep 8, 2012 #2
    Once you assume the direction, you have to be consistent with it.
    I quess you assume m2 is going down.
    Thus m2g is greater then 2T.

    Add: There 3 possibilities of movement. m1 or m2 or m3 accelerating downward.
    Last edited: Sep 8, 2012
  4. Sep 8, 2012 #3


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    Homework Helper

    Hoi jaw, welcome to PF.
    When m2 moves through a distance x in tthe downward direction, how much m1 and m2 move in the upward direction?
  5. Sep 9, 2012 #4


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    If m2 move downward by x
    Then should it be m1 move up by x/2 and m3 move up 1/2.
    Since string is constant <length

    Am I right?
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