A car has the following characteristics: weight = 18000 N; cross-sectional area = 2.5 m^2, drag coefficient = 0.5; rolling friction coefficient = 0.02. The energy content of gasoline is 3.5E10^7 Joules/Liter. The efficiency of fuel use varies with engine and drivetrain operation as described below.
(a) First consider highway driving. Assume a constant velocity of 27 m/s (60.4 mph) on level ground. Under these conditions the efficiency of the engine plus auxiliaries is 30 percent and the efficiency of the drivetrain is 85 percent. What is the fuel consumption in miles/liter under these conditions? Assume the density of air = 1.2 kg/m^3.
(b) Next consider city driving. As you know from your own experience, this is mostly start-stop driving. Assume that there are three start-stop cycles per kilometer of travel (five per mile). For each cycle the car starts from rest, accelerates up to 13 m/s (29.1 mph), then instantaneously stops. Under these conditions the net engine efficiency drops to 20 percent, and the drivetrain efficiency is 80 percent. What is the fuel consumption (miles/liter) for this city driving cycle?