Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How to find the Max. distance of the bungee jumper?

  1. Jan 16, 2005 #1
    Please help me to solve this question because I don't have a clue to do that!!

    Q: In a bungee jump a volunteer of mass 70 kg drops from a bridge, tethered to his jump point by an elastic cable of unstretched length L = 20m and elastic modulus 3000 N. Ifnoring energy losses, and assuming he hits nothing below, find the jumper's maximum distance of fall.

  2. jcsd
  3. Jan 16, 2005 #2


    User Avatar
    Science Advisor
    Homework Helper

    HINT:Use the law of conservation of mechanical energy.Pay attention with the 3 various types of energy the system has and with the "zero" for gravitational potential energy.


    P.S.The problem is posted twice... :grumpy:
  4. Jan 16, 2005 #3
    The total mechanical energy before the jump is equal to the total mechanical energy after the jump.

    The relevant equation is [itex]K_1 + U_{grav,1} = K_2 + U_{grav,2} + U_{el,2}[/itex].

    [itex]\frac{1}{2}mv_1^{2} + mgy_1 = \frac{1}{2}mv_2^{2} + mgy_2 + \frac{1}{2}ky_2^{2}[/itex]

    Choosing the relaxed hanging length of the rope as the origin,

    [itex]0 + mgL = mgy_2 + \frac{1}{2}ky_2^{2}[/itex].

    Exercise for the reader: find an equation relating the spring constant to the elastic modulus of the bungee cord and solve the above equation for [itex]y_2[/itex]. Hint: the distance of fall is not [itex]y_2[/itex].
  5. Jan 16, 2005 #4
    Potential energy for spring constant F=- kx, k=λ*A*x/L λ; however, now (A)cross-section area of the cord is provided; for string constant F = -λ (x/L). But will they equal?! kx = λ (x/L)?!

    Sorry, still not very understand!! :frown:
    Last edited: Jan 16, 2005
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook