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Homework Help: Average Net Force and G Force

  1. Jan 23, 2008 #1
    1. The problem statement, all variables and given/known data

    A 65 kilogram tightrope walker falls vertically downward with a velocity of 9.9m/s. She falls into a net which stretches 1.5m vertically as it breaks her fall. What is the average net force on the walker as her fall is being broken, and what is the G force that she experiences? Assume no air resistance.

    2. Relevant equations

    (Force)*(Change in Time) = (mass)*(Vf - Vi)
    (1/2)kx^2 ??

    3. The attempt at a solution

    Since I was not given an amount of time I am not sure how to start this problem. I know her Vf will obviously be 0 m/s. 9.9 m/s is her initial velocity. From this I can find that

    F*(change in time) = (65)(9.9)

    but I am still lost as to how to find force or change in time. I thought about using elastic potential energy (1/2 k*x^2) or gravitational potential energy (mgh) but I didn't see how this would help me (especially since I don't know the h).

    Could someone please give me some tips as to where to start?

    For G force I know that 1 G is equal to 9.81 m/s^2 but that is all.
  2. jcsd
  3. Jan 23, 2008 #2
    Err, is that all you're given?

    You just have to know her velocity when she reaches the net, so you need to know how far above it she is

    Then once you know her velocity when she reaches the net(maybe we're just assuming that it's 9.9m/s?)you know she has kinetic energy 1/2*mv^2

    Once the net is done applying a force to her over that 1.5m of distance, she will have had work done on her to cancel her kinetic energy(use W=F*d)
  4. Jan 23, 2008 #3
    Thanks...the problem just said that "her velocity is 9.9m/s" so I'm assuming that is velocity when she hits the net, otherwise, as I thought, it would be impossible to solve. Thanks for the help though...that does make more sense to do it that way.
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