A railcar with an overall mass of 66,000 kg traveling with a speed vi is approaching a barrier equipped with a bumper consisting of a nonlinear spring whose force vs. compression law is given by FS = x3, where = 640 106 N/m3 and x is the compression of the bumper. Treat the system as a particle. Assume that the contact between railcar and rails is frictionless, and let vi = 6 km/h