Calculating Closest Bungee Jump Distance

[snoitcelfer]

Homework Statement

an 80Kg bungee jumper steps off the jump platform which is 50m above the ground.
the bungee cord is 25m long when relaxed and has an E value of 8 MPa and a cross sectional area of 400mm^2.
Calculate the closest the jumper gets to the ground. Consider the center of gravity of the jumper to be at the end of the bungee cord.

Homework Equations

Energy conservation / strain energy

The Attempt at a Solution

i am stuck here because facing this problem i can find solutions using energy conservation such as mgh = (1/2)k(h-L)^2. however I have no idea how to get k from this as k = fx and i am not given a length with the jumper attached. so is it possible to find k from this information or do i need to go in a different direction?

 

[nvn]

snoitcelfer: Perhaps they want you to use the relaxed (initial) length L and assume k = E*A/L. But maybe someone will give a second opinion.