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Homework Help: Pulley problem with frictionless ropes

  1. Nov 12, 2011 #1
    1. The problem statement, all variables and given/known data
    In the diagram, the pulley is frictionless and the ropes are massless. You are given that m1 = 10.0 kg and m2 = 29.5 kg.

    Calculate the acceleration of m2 downwards.

    What is the magnitude of the tension in the string?

    2. Relevant equations

    sum of F= M*A

    3. The attempt at a solution

    I tried doing a free body diagram and solving for A but I still can't find the tension...
  2. jcsd
  3. Nov 12, 2011 #2
    You should post a picture of the pulley layout to make the problem clear.
  4. Nov 12, 2011 #3
  5. Nov 12, 2011 #4
    OK, you have written Newton's Law. Draw a free body diagram of each weight calling the tension in the rope T. You should have two equations. Let's see them.
  6. Nov 12, 2011 #5

    force of tension going up
    force of gravity going down


    m1: same thing ...
  7. Nov 12, 2011 #6
    Let's use some subscripts because the masses/weights are different:

    T - w1 = m1 * a

    T - w2 = m2 * a

    Looking at what you've written, you'll need to define what w1 and w2 are. Also, you have a single variable for acceleration. But the accelerations are in opposite directions so what must be done?
  8. Nov 12, 2011 #7
    So I have w1 and w2 and I have m1 and m2. Whats missing is T and A. Can I just solve for A or T ?
  9. Nov 12, 2011 #8
    Yes you can but if you do you'll get an incorrect result. You have an error in one of your equations. Acceleration, like 'g', has a direction associated with it.
  10. Nov 12, 2011 #9
    Signing off for today.
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