Airport runways are generally designed with a buffer zone around 300 m long beyo

Question

Airport runways are generally designed with a buffer zone around 300 m 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 132-m-long bed of crushable cement blocks.

What average force must this system exert on a 55-Mg jetliner that enters the arrestor bed at 36 m/s if the jet is to stop 100 m into the bed?

Take the direction of the plane to be positive. Express your answer using two significant figures.

Explanation / Answer

distance s = 120 m
mass m = 55 t = 55000 kg
velocity = 34 m/s

force f = ?

First let's find out the acceleration required using the formulas for constant acceleration. We have
s = (a * t^2)/2;
v = a * t;

Therefore
t = v / a
s = (a * v^2 / a^2) / 2 = 1/2 * v^2 / a
a = 1/2 * v^2 / s

And the force in newtons will be
f = m * a = 1/2 * m * v^2 / s = 1/2 * 55000 kg * (36 m/s)^2 / 120 m ~= 297000 kg*m/(s^2) ~= 297 kN

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