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Homework Help: Force clarification

  1. Oct 17, 2005 #1
    I'm just wondering if I'm doing this correctly..

    If I have something like this: http://img326.imageshack.us/my.php?image=pull6cx.png

    It's a closed system where the weights on the cart will get placed on the bottom holder for each trial... To find the 'force of the falling weight' I would take the mass*acceleration, where acceleration is determined by how fast the cart goes in a certain distance right? I wouldn't just take the mass*gravity when it's connected to a pulley like that would I?
  2. jcsd
  3. Oct 17, 2005 #2
    The only forces acting on the falling weight are Fg1 (force of gravity) and FT (force of tension in the rope). For the falling weight alone, Fnet1 = ma = Fg1+FT.

    Since FT is applied in both directions in the rope, it "cancels out" when you involve the entire system. For the entire system, Fnet = (m1+m2)a = Fg1+Ff2.

    Hope that helps.
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