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Homework Help: Newton's Third Law Problems

  1. Feb 13, 2012 #1
    Alright, so I have this sheet for homework and I'm not sure where to start.

    Incase you are unable to see, the questions say:

    a) What is the acceleration of the system and the tension in each rope if the girl lifts with a force of 100.0N?
    b) What is the force that she pulls with if T3 (bottom bucket) = 15.0N?


    To begin, I know I need to utilize the second law's equation F=ma, but I do not know which masses I am supposed to use to find Fg = gm.

    I need serious help, I am completely confused!
  2. jcsd
  3. Feb 13, 2012 #2


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    Homework Helper

    To find the acceleration of the system, you can replace the entire system by an equivalent mass M and a tension T.

    So M would be the sum of the 3 masses and T would T1+T2+T3 (they told you what 'T' was in the question.)

    Just formulate the resultant force and you should get it now.
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