1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Bungee jump- hard

  1. May 24, 2010 #1
    The girl is going on a bungee jump. She weighs 65 kg. The rope is 11m. In total, she fell 36 m. The first 11 m is free fall, and another 25m is simple harmonic motion.

    1) k of rope
    2)max spped
    3)what point when she has max speed
    4)amplitude of rope
    5)how long does it take

    2. Relevant equations
    vf^2= 2ax
    delta L= mg/k
    _/(k/m) A- square rt of k/m times A

    3. The attempt at a solution
    initial velocity = 0
    acceleration= 9.8m/s^2
    1) k of rope
    i got k for 25.48

    2)max spped
    max speed for free fall= 14.7m/s
    V_max for rope= 15.65m/s
    So do I add them up or just 15.65??!

    3)what point when she has max speed

    4)amplitude of rope

  2. jcsd
  3. May 24, 2010 #2
    why don't you show us how you solved each step, starting with the first one?
  4. May 25, 2010 #3
    1) i used deltaL= mg/k

    k= 25.48

    2) V_f^2=2(9.8)(11m)
    V_f=14.7m/s for free fall
    V_max= square rt of k/m *A
    so sqr (25.48/65) *25= 15.65 m/s

  5. May 25, 2010 #4
    ok, for part 1 you have it right, but try using a more accurate value for g = 9.81 m/s2. It will actually change your final answer.

    For part two, when do you expect the person to reach her final speed? And also, how did you derive "V_max= square rt of k/m *A"?
  6. May 25, 2010 #5
    V_max when the rope reach maxium stretch.
    I didnt derive it, it was a formula.
  7. May 25, 2010 #6
    oh i see what you meant now. but using kinetic and elastic energy relationships only holds when there is only an elastic force present for a given period of time. Is this the case?

    And plus, try to picture the scenario visually: once the elastic of the bungee jump is full stretched, what would you expect to happen? What would you guess her speed to be?
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook