# [Mechanics] Tension in bungee jumping

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1. Apr 24, 2016

### sushichan

1. The problem statement, all variables and given/known data
A bungee jumper of mass 60kg jumps from a bridge 24 m above the surface of the water. The rope is 12 m long and is assumed to obey Hooke's law. What should the spring constant of the rope be if the woman is to just reach the water?

2. Relevant equations
Ep=mgh
E=1/2 kx^2

3. The attempt at a solution
Energy conservation? I'm definitely doing something wrong here and not understanding something but I don't know what.

mgh = ½kx^2
(60)(10)(12) = ½k(12)^2
[I put the length of the unstretched part of the rope as my h value and x as the extension, which is 24-12=12]

k= 100 Nm^-1
[This is the answer I got]

But the answer is k=200 Nm^-2

2. Apr 24, 2016

### Staff: Mentor

To calculate the initial gravitational PE, use the height above the water.

3. Apr 24, 2016

### sushichan

okay thanks!

4. Apr 24, 2016

### atom jana

This is the key statement : The woman jumps from a bridge 24 m above the surface of water.