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Homework Help: Force Problem with weights

  1. Jun 4, 2010 #1
    1. The problem statement, all variables and given/known data
    A series of weights connected by very light cords are given an upward acceleration of 4.00 m/s2 by a pull P, as shown in Fig. 5.3.( a verticle strand of 4 balls with mass 5,10,15,and 20 kg with the pull at the top) A, B, and C are the tensions in the connecting cords.
    the pull P is closest to:

    290 N
    690 N
    50 N
    200 N
    490 N

    2. Relevant equations
    F= ma


    3. The attempt at a solution
    treating the weights as one mass
    Pull-mg=ma
    pull=m(a+g)
    = 552
    Which is not one of the answers. What is the error in my logic?
     
  2. jcsd
  3. Jun 4, 2010 #2

    collinsmark

    User Avatar
    Homework Helper
    Gold Member

    I'm don't see an error in your logic (if I'm interpreting your description of the figure correctly). :approve: Maybe there's an error in your calculations? :uhh: What did you use for m and g?

    [Edit: In other words, your equations seem fine. But I don't know why you ended up with 552]
     
  4. Jun 4, 2010 #3
    added the masses wrong xD Thank you.
     
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