The amount of energy a car expends against air resistance is approximately given by
where E is measure in Joules, ρairis the density of air (1.2 kg/m3), A is the cross-sectional area of the car viewed from the front (in m2), D is the distance traveled (in m), and v is the speed of the car (in m/s). Julie wants to drive from Tucson to Phoenix and get good gas mileage. For the following questions, assume that the energy loss is due solely to air resistance, and there is no wind.
Julie modifies her car, so that the effective cross-sectional area is reduced by 20%. How much further can she drive and still use the same amount of energy?