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Homework Help: Bunjee Jump Question

  1. May 23, 2010 #1
    1. The problem statement, all variables and given/known data
    A Year 12 Physics student has a mass of 85kg and is planning to bungee jump from a 200m high tower with a Killer Python Snake strapped to his ankles. The student decides to place his life in your hands and will totally rely on your knowledge of physics.

    He requests you to calculate the appropriate cross-sectional diameter of a 50m long Killer Python Snake, which is suitable to safely stop at least 20m above the ground below.

    2. Relevant equations
    Young's Modulus = 4854.37Nm^-2
    Strain = (Change in length)/(original length)
    Energy Absorbed = ((1/2)E.(ε)^2) x Volume
    Volume of a cylinder = (pi(r)^2 . L) r= radius, L = Length

    3. The attempt at a solution
    Here's my attempt :S

    GPE = MGH
    (85)(10)(180) = 153 000j

    Therefore the killer python must absorb at least 153 000j of energy before the student descends 180m. So i set energy absorbed ≥ 153 000

    and use equation:
    153 000 = ((1/2) E.(ε)^2). (pi (r)^2 .L) where E= young's modulus, ε = strain.
    153 000 = ((1/2) (4854.37).(2.6)^2)).(πr^2 .180)

    Solving for “r” gives:
    r ≥ 0.13

    Am i on the right track or is this wrong?
    Also, should i use length as 180 or 50 when calculating the volume?

    Cheers, Jay
    Last edited: May 23, 2010
  2. jcsd
  3. May 23, 2010 #2
    Any help or another method to go about this would be much appreciated.
  4. May 23, 2010 #3
    Is anyone able to help with this?
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