Finding spring constant and maximum acceleration

[chase222]

A 60 kg bungee jumper jumps from a bridge. She is tied to a 12 m long bungee cord and falls a total of 31 m. Calculate the spring constant of the bungee cord and the maximum acceleration experienced by the jumper.

I don't even know where to start. Can you tell me which equations I would use to find the answers to both parts of the problem?

 

[da_willem]

Find the formulas for the two forces involved, I suppose you can ignore friction which leaves you with how many forces? Then use Newtons F=ma to find the resulting acceleration, and note that the first 12m are a free fall...

 

[cepheid]

No, I won't tell you which equations to use. Instead, let's try to actually understand the problem: As always, start off with a free body diagram! What forces act on the jumper? It's easy...in this case there are only two. Gravity, and the restoring force of the bungee cord (it acts like a Hookian spring). So, what happens as she falls? Initially, the restoring force is zero. So gravity accelerates her downward. But the farther down she goes, the stronger the restoring force trying to pull her back up becomes. What happens at equilibrium? I.e. how can you determine what's going on at the point at which she stops falling? That's the key to solving this problem.