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Need an explanation on how to do a question applying Newtons Laws

  1. Oct 5, 2010 #1
    1. The problem statement, all variables and given/known data
    A 2.0 kg mass , placed on a smooth, level table, is attached by a light string passing over a frictionless pulley to a 5.0 kg mass hanging freely over the edge of a table. Calculate...
    a) the tension in the string
    b) the acceleration of the 2.0 kg mass on the table.


    The answer given was
    T=14N
    a=7.0m/s^2

    2. Relevant equations
    ΣF=ma


    3. The attempt at a solution
    ΣF=ma
    Ft + Fg = (5+2)a
    Ft + (mg) = (7)9.8
    Ft + (49) = (68.6)
    Ft = 19.6N
     
  2. jcsd
  3. Oct 5, 2010 #2

    PhanthomJay

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    Hello, Asimans, welcome to PF! Don't try to do this all at once.....look at each block separately. The acceleration is not 'g'. Note that the tension in a cord wrapped around an ideal pulley is the same on both sides of the pulley. Also note that the magnitude of the acceleration of each block must be the same in this example. So look at the lower block first, identify the forces acting on it, and apply your relevant equation. Then look at the other block, and do the same. What do you get?
     
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