- #1
tambourine
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Homework Statement
A 70 kg bungee jumper leaps off a bridge. She is tied to a 12 m long bungee cord and falls a total of 31 m. Calculate:
a) the spring constant of the bungee
b) the maximum acceleration experience by the jumper
Homework Equations
F = kx
Eg = Ee
where g is gravitational potential energy and e is elastic energy
The Attempt at a Solution
at her maximum stretch, force of the "spring"/bungee Fs = Fg = mg
x= 31 - 12 = 19
k= F/x = mg/x
k = 70 (9.81) / 19
k= 36.14
but this number didn't seem right so i did:
let height be zero at maximum stretch
Eg = Ee
mgh = 1/2kx^2
70(9.81)(31) = 1/2k(19)^2
k = 117.9
both methods make perfect sense to me, but the spring constants are different so i must have missed something. what did i do wrong/which method is correct? and how can i find her maximum acceleration?