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Bungee Cord Force Constant from Work?

  1. Oct 1, 2009 #1
    1. The problem statement, all variables and given/known data
    A bungee jumper jumps with a mass of 61kg jumps off of a bridge. The massless bungee cord is 25m long and beyond that length acts as a spring. The jumper reaches the lowest point 42.9m below the bridge. Find the force constant which characterizes the bungee cord.


    2. Relevant equations
    W = F X d
    F = -kx

    3. The attempt at a solution
    First I calculated the work for mg.
    Wmg = 42.9 * 61(9.8) = 25646J

    Since the object stops, the object has a net work of zero. So:
    -25646 = 17.9 * F
    F = -1433N

    -1433 = -k(17.9)
    k = 80N/m.

    This seems far too low, could someone please tell me where my logic is flawed? I think it might be In the assumption that balancing net work accounts for the object stopping but i am not sure.

    Thanks in advance!
     
  2. jcsd
  3. Oct 1, 2009 #2

    ehild

    User Avatar
    Homework Helper
    Gold Member

    The force exerted by a spring is not constant, as you assumed.

    ehild
     
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