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Magnitude of acceleration of bricks. please help

  1. Sep 23, 2007 #1
    Magnitude of acceleration of bricks. please help!!!

    A load of bricks with mass1 = 16.0 kg hangs from one end of a rope that passes over a small, frictionless pulley. A counterweight of mass2 = 28.6kg is suspended from the other end of the rope. The system is released from rest.

    What is the magnitude of the upward acceleration of the load of bricks?

    What is the tension in the rope while the load is moving?


    Draw two free body diagrams with the forces acting on each. I did. You need to find the Sum of the y forces on each and this is where I get lost. I know its Sum of y forces = ma but I dont know what to do from there.

    Please help me! Thank you!
  2. jcsd
  3. Sep 23, 2007 #2


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    Staff: Mentor

    We know that the tension T in the rope must be equal on both sides of the pulley, and we know that W1 = m1g and W2 = m2g are acting downward.

    Now, m2 > m1 so m1 must accelerate upward and m2 must be accelerated downward at the same rate.

    This is the principle of Atwood's machine.

    Write the two equations, one each for each mass. T is upward for both, W is down, and then there is the net force on each mass which must equal the difference between T and the respective W.
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