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Homework Help: Tension of a string with a pulley

  1. Sep 21, 2010 #1
    1. The problem statement, all variables and given/known data
    Two masses are connected by a string over a pulley as shown below. The incline is
    frictionless and makes a 50 degree angle from the horizontal. If m1 = 3.00 kg and m2 = 8.00 kg, find the tension in the string.

    ZUrQB.png


    2. Relevant equations
    F = ma


    3. The attempt at a solution
    I thought the tension in the string would be the same as the weight of m1, which is 29.4N, but that is not the correct answer. I am not sure what to try from here.
     
  2. jcsd
  3. Sep 21, 2010 #2
    m1 accelerates, so you need to take that into consideration.
    First write up the equations of motion of the two blocks.
    i.e. m1*a=...
    and m2*a=...
     
  4. Sep 21, 2010 #3
    I got that that a equals 2.79m/s², so:

    m1*a = 3 * 2.79 = 8.37N
    m2*a = 8 * 2.79 = 22.32N

    Is that what you mean? Is that right?
     
  5. Sep 21, 2010 #4
    Yes, and now you can express the tension of the string. m1*a=m1*g-T
     
  6. Sep 21, 2010 #5
    That got me the correct answer! Thanks so much for your help!
     
    Last edited: Sep 21, 2010
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