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Homework Help: Finding g from Atwood's Machine

  1. Sep 24, 2010 #1
    1.The problem statement, all variables and given/known data

    Two masses hang from a string running over a pulley. Such a device can be used to measure the acceleration of gravity; it is then called Atwood's machine. If the masses are nearly equal, then the a of the masses will be much smaller than g; than makes it convienient to measure a and then calculate g. Suppose than an experimenter using masses m1= 450g and m2=452g finds that the masses move a distance of 0.472m in 5.8s starting from rest. What value of g does this imply? Assume the pulley is massless.

    2. Relevant equations
    I know that a=(m2-m1/(m2+m1))g

    3. The attempt at a solution
    From the above equation, I know that a=0.0022g
    When using a=2y/t2, though I get g=12.8m/s/s, which is wrong (online hw).
    Can anyone point me in the right direction?
  2. jcsd
  3. Sep 24, 2010 #2


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    Gold Member

    yes, but you should derive that equation instead of looking it up.
    I get g=12.6, which probably in either case should be rounded to 2 significant figures, g=13m/s/s.. Looks like there was a lot of experimental error in that setup.
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