1. The problem statement, all variables and given/known data Matt(44kg) was going to do a bungy jump(spring constant=105N/m) that is 30m long when it's unstreched.The rope is attached to a platform 65m above the ground.What is the maximum acceleration closes to the ground. Sorry for my bad english, i was trying to translate my homework from swedish to english. 2. Relevant equations Don't know 3. The attempt at a solution I'm using the conservation of engery rule thing. Ep+Ek+Es=E2p+E2k+E2s There is no kinetical energy or spring energy in the beginning, and no potential or kinetical energy in the end => Ep=E2s => mgh=1/2*k*x^2 and we don't know the total lenght => mg(h+x)=1/2*k*x^2 and then i solve x and i get that x= about 20m so the total lenght when the string is attached is 20+30=50m And then i can solve the force of the spring, F=k*x F=105N/m*50m F=5250N And then i use ƩF=m*a => G-F=m*a => (G-F)/m=a => (44kg*9,81m/s^2-5250N)/44kg=-109,508 m/s^2 And this can't be true! Any ideas?