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Homework Help: Help with Newtons Law Pulley Problem

  1. Feb 5, 2007 #1
    1. Two blocks are connected by a rope that passes over a set of pulleys. One block has a weight of 412N, and the other has a weight of 908N. The rope and the pulleys are massless and there is no friction. a.) What is the acceleration of the lighter block? b.) Suppose that the heavier block is removed and a downward force of 908N is provided by someone pulling on the rope. Find the acceleration of the remaining block. c.) Explain why the aswers in a and b are different.

    a= m2-m1 / m2+m1 * g

    For part a, I found the following. a= 908-412 / 908+412 * 9.80 = 3.68m/s. Is this correct. For part b, how would the answer be different from part a if you are applying the same amount of force and pulling it in the same direction. I'm confused.
  2. jcsd
  3. Feb 6, 2007 #2


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    The question says "the heavier block was removed". So the new equation of motion only has one mass, not two.

    In the first part, the tension in the rope was not 908N. If you draw a free body diagram for the heavy mass, you have its weight of 908N, the tension T in the opposite direction, and the resultant force of (908-T) causes the accleration of 3.68 m/s^2.
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