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Homework Help: Bungie jumper jumps of cliff. (Energy)

  1. Mar 18, 2012 #1
    1. The problem statement, all variables and given/known data
    A 55 bungee jumper leaps from a bridge. She is tied to a bungee cord that is 11 long when unstretched, and falls a total of 31 .
    a)Calculate the spring constant of the bungee cord assuming Hooke's law applies.
    b)Calculate the maximum acceleration she experiences.

    3. The attempt at a solution
    first i drew out the problem in 3 sections. the first (A) the jumper on a cliff 31 m above h=0, then i drew (B) the jumper 11 m below the cliff because that is the length of the rope, and the third (C) the jumper at h=0, all the way at the bottom.

    a)= 84 N/m
    -to get this i solved for velocity at B by setting the energy at A = energy at B. mgh(at A)=1/2mv^2+mgh(at B) and got v=14.7 m/s. then i used Energy at B=Energy at C, mgh(at B)+1/2mv^2=1/2kx^2 and got k=83.5 N/m.

    b)i know the point of greatest acceleration cant be at A, at B its simply acceleration due to gravity, and at C the jumper is at h=0 and has a moment of no movement, so no acceleration. however the answer isn't 9.8.
  2. jcsd
  3. Mar 18, 2012 #2
    For part B), don't forget that DECELERATION is also acceleration, simply in the opposite direction of velocity. The acceleration required when she is stopped at the bottom of the cliff is much greater than 9.8.
  4. Mar 18, 2012 #3
    true. ima give that idea a try
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