1. The problem statement, all variables and given/known data Starting from rest, a 64.0 kg person bungee jumps from a tethered balloon 65.0 m above the ground. The bungee cord has negligible mass and unstretched length 25.8 m. One end is tied to the basket of the balloon and the other end to the person's body. The cord is modeled as a spring that obeys Hooke's law with a spring constant of 81.0 N/m, and the person is considered to be a particle. The balloon does not move. Find an equation for the total potential energy of the system as a function of height y above the ground and determine the minimum height the person will be above the ground during the plunge. 2. Relevant equations Gravitational potential energy is modeled as U = mgy and elastic potential energy is modeled as U = .5ky^2 3. The attempt at a solution So I thought the gravitational potential equation was straightforward; U = (64)(9.8)y. For the elastic potential equation I am not so sure; I wrote down: U = .5(81)(39.2 - y)^2 since the tether hangs unstretched 39.2 m above the ground. And again, I am not totally sure but the total potential energy equation should simply be the sum of those two equations; U = 627.2y + 40.5(39.2 - y)^2. Even if this equation is correct, I do not know how to find the minimum height of the jumper; is it when the potential energy is 0 J? Any help would be appreciated.