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Homework Help: Conservation of Energy bungee jumping

  1. Nov 4, 2007 #1
    1. The problem statement, all variables and given/known data
    A bored college student decides to try bungee jumping. He attaches an elastic bungee cord to his ankles and happily jumps off a tall bridge across a river. He ends up barely touching the water before the cord jerks him back up

    The length of the relaxed cord is y_e; the distance from the bridge to the river surface is y_0 (where y_o>y_e), and the spring constant of the elastic cord is k.

    Which assumptions are reasonable to make in this problem?

    a.The student can be treated as a particle moving with constant speed.
    b.The student can be treated as a particle moving with constant acceleration.
    c.The student cannot be treated as a particle.
    d.The air resistance is substantial.
    e.The air resistance is negligible.
    f.The amount of heat generated in the bungee cord is substantial.
    g.The amount of heat generated in the bungee cord is negligible.
    h.The bungee cord applies a constant (or zero) force on the student.
    i.e bungee cord can be modeled as a spring that obeys Hooke's law.

    2. Relevant equations
    no equations

    3. The attempt at a solution

    I tried BEGI, CEGI, BEGH, AEGI. And they are all wrong. I need help.
  2. jcsd
  3. Nov 4, 2007 #2


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    Homework Helper
    Gold Member

    I agree with you third answer AEGI, other than A. Why would the person move with a constant speed?
  4. Nov 4, 2007 #3


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    Staff Emeritus
    Science Advisor

    Please don't multi-post. Please delete the other post of this problem.

    Also, please show some work or effort in answering each of these points.

    If one is familiar with the geometry of the bungee problem, it starts with the bungee cord folded in half, one end attached to a person (the mass) and the other end fastened to a hopefully immovable object such as a building or bridge.

    Now until the bungee cord unwraps to its full length, the person (mass) is in freefall under the influence of gravity. When the bungee cord starts stretching, it applies a force which decelerates (slows) the falling mass.

    I suggest writing the equation for the spring force of the bungee cord.

    Also write the one's thoughts on air resistance and heating of the bungee chord.
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