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A man who does bungee jump jumps by the platform. The mass of the man is 60Kg . There is 45m from the platform to the water. Without stretching the rope is 25m long. The spring constant(k)=160Nm-1. What is the extention of the robe?

Attempt to solve

F=ke

The man has a gravitational force of 60*9.8N and so F=60*9.8N

So e=(60*9.8)/160

e=3.675m

But there is a mistake in my attempt. I can't find where it is. Can you help me for find the mistake?

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closed as off-topic by sammy gerbil, M. Enns, ZeroTheHero, John Rennie, heather Aug 27 '17 at 14:34

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What you calculated is the extension of the rope when the man is not bouncing anymore, i.e. just hanging by the rope.

To calculate the maximum extension during the jump it would be easiest to consider conservation of energy.

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The error lies in the fact that equalizing the forces results in zero acceleration, i.e. constant velocity. You instead need to solve for the maximum extension of the rope, which is the first time velocity equals zero. You can accomplish this by also considering the potential energies.

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