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Homework Help: Newton's Laws pulley homework

  1. Feb 20, 2010 #1
    1. The problem statement, all variables and given/known data

    The 100 kg blcok in the figure takes 5.40 s to reach the floor after being released from rest. What is the mass of the block on the left?
    knight_Figure_08_33.jpg

    2. Relevant equations
    F=ma
    sf=si + (1/2)(a)(delta t)


    3. The attempt at a solution

    I know to find acceleration you use
    sf=si + (1/2)(a)(delta t)
    0=1+(1/2)(a)(5.4)
    a = 0.0686 m/s2

    and then the F=ma to find the force on the block of known mass.
    F=(100 kg)(0.0686)
    F=6.86

    but from this I am not sure how to determine the mass of the block on the left?
     
  2. jcsd
  3. Feb 20, 2010 #2

    tiny-tim

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    Science Advisor
    Homework Helper

    Welcome to PF!

    Hi redlightgreen! Welcome to PF! :smile:

    Find the tension, T, and then use the fact that the block on the left has the same acceleration (in the opposite direction, of course). :wink:
     
  4. Feb 20, 2010 #3
    oh okay! thank you so much.
    i've got it now!
     
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