physics
posted by Steven .
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?
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.

potential energy decrease in fall = potential energy put into spring
m g h = (1/2) k h^2
h = 2 m g /k 
i think we will get from your way damon h be about 15.68 which is wrong..

no no your correct but correct answer will bet putting h3 in place of h..

Oh, yes, sorry

so whats the correct 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 (h3) = 1/2 k x^2.
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