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Homework Help: Newton's Secon Law

  1. Nov 3, 2007 #1
    1. The problem statement, all variables and given/known data
    Two buckets of nails are hung on above the other and are pulled up to a roof by a rope. Each bucket has a mass of 5.0 kg. The tension in the rope connecting the buckets is 60 N. Calculate the acceleration of the buckets.

    2. Relevant equations
    F = ma

    3. The attempt at a solution
    Here is my work:
    http://img233.imageshack.us/img233/3691/fbd2ke5.jpg [Broken]​

    I got the answer right, but I don't know why mass is equal to 5kg. Shouldn't it be equal to 10kg, because there are two masses of 5kg?
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Nov 3, 2007 #2


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    The ropes are attached together so they are going to accelerate at the same rate. It looks like what you did up there is find the acceleration for the lower bucket. 60N is the tension in the rope connecting the buckets, but not the force the top bucket is being pulled up with, since some force will accelerate the top bucket, and then whats leftover will go into the rope. So, the work you have there is essentially finding the acceleration for the lower bucket, but this is ok, since the buckets are going to accelerate at the same rate.
  4. Nov 3, 2007 #3
    But if the top bucket is a different mass than 5 kg, could I still use the same procedure that I used in this question, to find the acceleration of the buckets? Also, do I need to use both masses in my calculation when solving for acceleration?
  5. Nov 4, 2007 #4
    Can someone help me some more on this question please?
  6. Nov 4, 2007 #5


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    If you look at the bottom bucket only in a free body diagram, as you have done, and as GO1 has noted, you get the acceleration without having to look at both buckets togeteher. Once you determine that acceleration, you can find the force in the upper rope, if you wish, using both masses together in your FBD.
    Last edited: Nov 4, 2007
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