Suppose a car travels 108 km at a speed of 33.0 m/s and uses 1.8 gal of gasoline. Only 30% of the gasoline goes into useful work by the force that keeps the car moving at constant speed despite friction. (The energy content of gasoline is 140 MJ/gal.)
(a) What is the magnitude of the force (in N) exerted to keep the car moving at constant speed?
(b) If the required force is directly proportional to speed, how many gallons will be used to drive 108 km at a speed of 24.0 m/s?