Find the average force?

Airport runways are generally designed with a buffer zone around 300m long beyond the runway end, to accommodate aircraft that land too fast or too far down the runway and go off the end. Where that's not possible, airports are increasingly installing so-called Engineered Material Arresting Systems (EMAS) to prevent runaway aircraft from entering nearby roads, neighborhoods, or waterways. One such system, at New York's JFK airport, consists of a 132m--long bed of crushable cement blocks. What average force must this system exert on a 55-Mg jetliner that enters the arrestor bed at 36m/s if the jet is to stop 120m into the bed?