Calculate Force Constant for Bungee Jumping

[blader324]

Homework Statement

so i have a bungee jumper starting 36m above the surface of a river from a hot air ballon. the elastic cord is attached to his waist. the unstretched length of the cord is 25m, and the student weighs 700N. calculate the required force constant of the cord if the student is to stop safely 4m above the river.

Homework Equations

The Attempt at a Solution

i tried using the conservation of mechanical energy at the top of the balloon to 32 meters below the balloon because that's where the guy wants to stop. also i know that the cord has to stretch 7 meters in order for him to stop 4 meters above the river.

 

[Kurdt]

Its a lot like spring constants and stretching of springs. Once the guy reacheas 25m below the balloon his bungee cord will be fully extended but unstretched. At this point he will have some kinetic energy which needs dissipating in a certain distance. Do you know the potential energy of a stretched spring?

[Of course assuming the bungee cord behaves like a spring.]

 

[blader324]

thanks so much, i figured it out as soon as i got to class!