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Homework Help: Atwood's Machine

  1. Apr 27, 2010 #1
    1. The problem statement, all variables and given/known data
    The two masses (m1 = 5.2 kg and m2 = 2.6 kg) in the Atwood's machine shown in The Figure are released from rest, with m1 at a height of 0.79 m above the floor. When m1 hits the ground its speed is 1.7 m/s.

    Assuming that the pulley is a uniform disk with a radius of 12 cm, outline a strategy that allows you to find the mass of the pulley.

    Determine the pulley's mass.

    2. Relevant equations
    Rotational Kinetic Energy: K + (1/2)Iw2
    Conservation of Energy: Ki + Ui = Kf + Uf

    3. The attempt at a solution
    I am more or less stumped on this problem. Information that is known is that v0 = 1.7 m/s and vf = 0. The Ei = mgh (I think since the system starts at rest and m1 has Gravitation Potential Energy). Ef = (1/2)mv2 + (1/2)Iw2. All this is speculation since I am grasping at a way to solve this problem.

    Also, from looking at other related problems people tend to find acceleration through the Kinematics v2 - v02/2(x - x0). However, I am not sure how to apply the acceleration of m1, all I know is that it translates through the pulley system.

    Another possible acceleration I found was a = [(m1 - m2)/(m1 + m2)]g. This formula brought up a different acceleration than the previous, but once again I am not certain how to apply it.

    Reassurance that I am on the right route, and a hint would be greatly appreciated.
    Last edited: Apr 27, 2010
  2. jcsd
  3. Apr 27, 2010 #2
    What is the question? Your problem is nothing but stated facts, and there is no question. Literally, not a single question mark.
  4. Apr 27, 2010 #3
    Thank you for bringing that to my attention. I have spent so much time belaboring the issue through my mind that I completely forgot to actually spell out the question.

    Although, no question marks does not mean there exist no questions.
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