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Massless strings/pulleys: Finding the magnitude of the Force

  1. Oct 20, 2008 #1
    1. The problem statement, all variables and given/known data
    A massless string runs around two massless, frictionless pulleys, as shown in the figure below. An object with mass m = 10.3 kg hangs from one pulley. A force F is exerted on the free end of the string. What is the magnitude of the force F if the object is lifted at a constant speed?

    2. Relevant equations
    I'm guessing around 1/2m x v^2 but I really don't have a clue...

    3. The attempt at a solution
    Well so far I got that the force goes in the y axis so that he factors involving the y axis is the weight and tension. Since the question does not give me tension and I really don't know what formula to use to figure it out I'm quite lost.

    There's also a diagram but I dunno how to put it up here...
  2. jcsd
  3. Oct 20, 2008 #2
    Can you try to describe the figure? Give the path of the string and position of the pulleys and mass, if you can.

    Also, (1/2) m * v2 will give you units of work or energy. It sounds more like you need an equation dealing with force, mass, and acceleration.
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