1. The problem statement, all variables and given/known data A bungee jumper of mass m drops off a bridge and falls vertically downwards. The bungee cord is elastic with natural length L and stiffness k. Deduce that at the lowest point of the fall, the cord is stretched by an amount: x=mg/k(1+√(1+(2kl/mg)) 2. Relevant equations F=-kx PE=mgh=0.5kx2 Where h=L+x 3. The attempt at a solution The total energy before the jump is equal to the total energy after the jump. Since at the bottom there is no kinetic energy I said the Potential Energy before is equal to the Elastic Energy at the bottom. So: mg(L+x)=0.5kx2 x2=(2mgx +2mgl)/k x=√((2mgx +2mgl)/k) I'm having problems here trying to get in the asked form. Have I forgotten something n the conservation of energy?