A bungee jumper jumps from a bridge with a 3 m long bungee cord. Once the cord starts to stretch, it acts like an ideal spring with coefficient of elasticity k=100 N/m. What should be the minimum height of the bridge in m so that this jump is safe for the jumper?

Question

Details and assumptions
The jumper has a mass of 80 kg.
The acceleration of gravity is −9.8 m/s^2.
There are at least two ways to solve this problem.
Treat the jumper as a point mass at the end of the cord.

Damon · Answer

potential energy decrease in fall = potential energy put into spring m g h = (1/2) k h^2 h = 2 m g /k

Steven · Answer

i think we will get from your way damon h be about 15.68 which is wrong..

Steven · Answer

no no your correct but correct answer will bet putting h-3 in place of h..

Damon · Answer

Oh, yes, sorry

steven · Answer

so whats the correct answer?

Ozone · Answer

The correct answer is 21.276 Consider the law of conservation of energy in solving this problem. i.e. gravitational potential energy = elastic potential energy. So, m g (h-3) = 1/2 k x^2.