From a test I had: A 700N bungee diver is released from a 40m bridge attached to a bungee cord which is 25m when unstretched. The cord obeys Hooke's Law. Find the spring constant of the cord if the diver is to stop 4m above the surface. What I did was say that gravity pulls this diver down 36m, and W=Fd=700*36. Now, when the cord actually gets him stopped, all that energy is potential spring energy, and with the distance the cord is stretched from equilibrium being 11m, 1/2kx^2 = mgh is easy to find. I ended up with 416N/m. However, the only force acting on the diver is gravity from 0 to 25m. From 25 to 36m, though, the cord is acting. But, isn't the cord only acting to decrease the Ke gained during the 25m fall, and to also decrease the GPE the diver has as he continues to fall from 25 to 36m?? Or did I do this right and all the energy that the cord has at the bottom of the fall is solely due to gravity, thus, mgh?