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Uniform circular motion issue

  1. Feb 7, 2008 #1
    1. The problem statement, all variables and given/known data
    A woman rides on a Ferris wheel of radius 16 m that maintains the same speed throughout its motion. To better understand physics, she takes along a digital bathroom scale (with memory) and sits on it. When she gets off the ride, she uploads the scale readings to a computer and creates a graph of scale reading versus time. Note that the graph has a minimum value of 510 N and a maximum value of 666 N .

    What is the woman's mass?

    2. Relevant equations
    Period = 22s

    3. The attempt at a solution
    Woman velocity/acceleration:
    Velocity= 2pi(16)/22 = 4.57 m/s
    Acceleration=(4.57)^2/16 = 1.31 m/s^2

    i am stuck here, can't figure what equation to use next.
    i think this might be it
    Fnet=ma = m (v^2/R)
  2. jcsd
  3. Feb 7, 2008 #2


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    Talking in terms of centripetal 'forces', the force on the scale at the top is mg-mv^2/r=510N and the force at the bottom is mg+mv^2/r=666N. If you subtract those you can solve for mv^2/r and then use your value for v^2/r to solve for m. Alternatively, you could add them and solve for mg. You should get about the same thing. So you never actually needed to know the radius and rotation rate of the wheel. I'd suggest you do the former though, since that's probably what they want to do.
  4. Feb 7, 2008 #3
    i solved it.
    answer: 60kg.
  5. Feb 7, 2008 #4


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