a) Determine an expression for the work done by the force F as a function of x. An uncontrolled 1000 kg car strikes squarely a motorway crash cushion in which the car is brought to rest by successively crushing steel barrels. The length of the crash cushion is 5.4 m, and the magnitude F of the force required to crush the barrels as a function of the distance x the car has moved into the cushion is given by 75kN 120kN 170KN (0 ≤ x ≤ 1.1m) (1.1 ≤ x ≤ 3.6m) (3.6 ≤ x ≤ 5.4m)