Starting from rest, a 64.0 kg person bungee jumps from a tethered balloon h = 65.0 m above the ground. The bungee cord has negligible mass and unstretched length L = 27.1 m. One end is tied to the basket of the balloon and the other end to a harness around the person's body. .(a) Express the elastic potential energy of the cord, Us, as a function of y for points below y = h - L = 37.9 m. (Use m, g, h, L, k, and y as necessary.) (b) Express the total potential energy of the person-cord-Earth system as a function of y for points below y = 37.9 m. (Use m, g, h, L, k, and y as necessary.) (c) Assume that air resistance is negligible. Determine the minimum height of the person above the ground during his plunge. (d) Does the potential energy graph show any equilibrium points or positions? If so, at what elevations? Are they stable or unstable? what is equilibrium at Y? (e) Determine the jumper's maximum speed.