The roads used by quarry trucks were not repaired for years and resemble washboard?

Question

Empty trucks (m=5 tonnes) arrive at speed 30 km/s, load 15 tonnes of ore, and depart at speed 20 mph.

Period of the bumps on the road leading to the quarry is about 12m.
What is period of bumps on the road leading out of the quarry?

Answer 1

Assuming negligible unsprung weight, the loaded period of vibration will be twice the unloaded period, period being proportional to sqrt(m/k). So the bumps (generated by a form of feedback resonance) will be 12 * 20/30 * 2 = 16 meters in period.