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Homework Help: 2 equal masses raised on pulley at constant velocity, what is the force ?

  1. Nov 21, 2012 #1
    1. The problem statement, all variables and given/known data

    2 equal masses (massA, massB) are raised up a pulley, at a constant velocity. massB has a velocity twice as fast as massA. What is the force acting on these 2 masses?

    2. Relevant equations

    3. The attempt at a solution

    If it is a constant velocity, the upwards force must be equal to mg correct? So Fa=mg, Fb=mg. But if this is the case, how is it possible massB moves twice as fast as massA with out an additional force acting on it?

    I am confused, can anyone out there help me please?
  2. jcsd
  3. Nov 22, 2012 #2

    Simon Bridge

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    Hint: what do pulleys do? What are they for?

    Note: a net zero force is needed to move at any constant speed - so two equal masses can have the same applied force and yet move at different constant speeds. You get different speeds by applying, for eg., the same unbalanced force for different amounts of time. But I don't think they are talking about the force on the mass - but the force applied to the end of the rope.

    (However: I don't think all that is all the information you are given.)
  4. Nov 22, 2012 #3
    No it is not all the given info. It was a power question but I got it figured out. I was just confused about the part where it could be any speed. But now it seems like a silly question now that I understand. Thanks though!
  5. Nov 22, 2012 #4

    Simon Bridge

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    Once you understand something, earlier confusion often appears silly.
    We are all wise in hindsight ;)
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