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Equation for the tension in the string

  1. Mar 12, 2005 #1
    Two objects A and B hang down on either side of a smotth pulley, connected by an inextensible string. The masses of the objects are 3m and km respectivly. A accelerated at 2/5g when released. g=9.8N. What is the value of k.
    I worked it out to be 1.29, by writing an equation for the tension in the string for both objects. But the the value of k is supposed to be greater than 3. :confused: Did I use the wrong method?
  2. jcsd
  3. Mar 12, 2005 #2

    Doc Al

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    Staff: Mentor

    What direction does A accelerate? You assumed down, and got the correct answer for that assumption. If km > 3m, then A would accelerate up. Try making that assumption and solve for k.
  4. Mar 12, 2005 #3
    yes. This time round I get k=7? Is this right?
  5. Mar 12, 2005 #4
    Oh right. I didnt read the question properly. if k is bigger than 3, then obviously its the greater mass. Thanks for clearing my problem.
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