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Homework Help: Newton and pulley problem

  1. Nov 11, 2005 #1
    a 3kg object sits on table with a pulley attached to it. there is a M object hanging from the pulley. dropped from rest the system moves 127.5cm in 1.65951s. there is no friction. what is the value of the mass M.

    i used x=vot+1/2at^2 to find the accleration of the 3kg object. it is .9729m/s^2. T=ma=2.77. for the M object, is it T=W?
  2. jcsd
  3. Nov 11, 2005 #2
    I'm assuming that the pulley is supposed to be massless here. Since this is a frictionless case, by drawing a free-body diagram, we see the only force acting on the 3 kg mass, m, is the tension, and the tension in the rope is uniform. Drawing a free-body diagram for mass M, the total force on it downward is T- Mg. Force on the 3 kg mass is ma, and you've solved for a already.

    ma = Mg - T (T - Mg instead depending on the situation)

    However, remember that v_0 is your initial velocity in the x direction. This doesn't equal the distance/time. The system starts from rest.
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