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Homework Help: Atwood's Machine Help

  1. Feb 28, 2010 #1
    1. The problem statement, all variables and given/known data

    ok heres the problem in a picture

    h t t p : / / i m g 1 9 2 . i m a g e s h a c k . u s / i m g 1 9 2 / 4 5 0 0 / c a p t u r e x x w . j p g



    2. Relevant equations

    Sigma F = ma
    Fg = mg
    3. The attempt at a solution

    ok I called the 4 kg block m3 and the 2 kg block m2 and the 1 kg block m1

    I don't see what is wrong with my work

    a. net force on m3 = m3 a = Fg3 - Fg2 - Fg1

    divide by m3 to get a

    a = (Fg3 - Fg2 - Fg1)/m3

    made it look nice

    a = (m3 g - m2 g - m1 g)/m3
    = g - (m2g)/m3 - (m1 g)/m3
    = g(1 - m2/m3 - m1/m3)
    =9.8(1 - 2/4 - 1/4) = 2.5 m/s^2

    b. net force on m3 = m3 a = Fg3 - Ft3
    solved for the force of tension
    Ft3 = -m3(a+g) = -4.0(2.5+9.8)= - 49 N

    c. Net force m1 = m1 a = -Fg1 + Ft1
    solved for Ft1
    Ft1 = m1 (a+g) = 1.0(2.5 + 9.8) = 12 N
     
  2. jcsd
  3. Feb 28, 2010 #2
    i think i got it nevermind
     
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