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Homework Help: Gr 12 Atwood Machine Lab

  1. Mar 6, 2006 #1
    im stuck on the last question of this lab. "what combination or masses would make the accelration of an atwood machine equal to 1/2 g?"

    a = g (m1 - m2/m1=m2)

    so i have to find out what m1 and m2 are eual to in that forumula if g = 1/2

    im thinking a is equal to 9.81 because the accelration on an atwood machine is caused by gravity

    im stuck help would be nice:rofl:

    ive tryed rearangeing forumlas but i hvant got anywhere yet
  2. jcsd
  3. Mar 6, 2006 #2
    I think you're a bit confused because near the surface of earth g is always about 9.8. So you have the formula for acceleration which is correct and you want that to be equal to (1/2)*g so if you set those equal the "g"s on both sides will go away and you should be able to figure something out as to what ratio the masses must be in relative to each other in order to get an acceleration of (1/2)g
  4. Mar 6, 2006 #3
    still hvaing hard time here if i plug in 1/2 for g and 1/2 for a i end up with m1-m2 = m1 + m2
    nothing in clicking yet im having a rough time here
  5. Mar 6, 2006 #4
    g is a constant. What does that mean? You cannot plug a value in for g, near the surface of earth g is always about 9.8. You want the acceleration to equal (1/2)g so plug that in for a, and then look at teh equation resulting.
  6. Mar 6, 2006 #5
    Look at the sum of the forces on the masses of the atwood machine
    [tex] T-m_{1}g=m_{1}a \hspace{0.5cm} -T+m_{2}g=m_{2} a [/tex]
    Now add the two equations together, and you get an expression in terms of the coupled acceleration, gravity and masses. Now eliminate gravity, with desired acceleration
    [tex] g =2 a [/tex]
    and now we have an equation totally in terms of the masses, which allows us to solve . hope this helps, sincerely, x
  7. Mar 6, 2006 #6
    meh ok i figured it out it was really simple actually and i was going about the problem wrong im jsut tired haha
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