When a bungee jumper jumps, ignoring the mass of the bungee cord, the jumper initially falls in freefall before an inelastic collision occurs between the jumper and cord, and the cord extends as the jumper continues to accelerate downwards.
The only force acting downwards on the jumper is their weight. The extension of the cord when the jumper and cord are in their equilibrium position is given by e = F/k (Hooke's law). Given that the force acting downwards is constant (the jumper's weight), why does the cord continue to extend beyond this equilibrium extension as the jumper moves downwards? What force is further extending it? Why doesn't the jumper come to an instantaneous rest (implausible as this clearly is)?