Posted by Steven on Tuesday, July 23, 2013 at 12:52pm.
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.

physics  Damon, Tuesday, July 23, 2013 at 12:55pm
potential energy decrease in fall = potential energy put into spring
m g h = (1/2) k h^2
h = 2 m g /k 
physics  Steven, Tuesday, July 23, 2013 at 1:07pm
i think we will get from your way damon h be about 15.68 which is wrong..

physics  Steven, Tuesday, July 23, 2013 at 1:11pm
no no your correct but correct answer will bet putting h3 in place of h..

physics  Damon, Tuesday, July 23, 2013 at 1:13pm
Oh, yes, sorry

physics  steven, Tuesday, July 23, 2013 at 7:12pm
so whats the correct answer?

physics  Ozone, Saturday, July 27, 2013 at 12:56pm
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.