Fuel used to counter air resistance The resistive drag force that the air exerts on...

Fuel used to counter air resistance The resistive drag force that the air exerts on an automobile is

F _{Air on Car} = (1/2)CApv²

car is, r is the density of the air, A is the cross-sectional area of the car along its line of motion, and v is the car’s speed relative to the air. Consider the effect of air resistance on fuel consumption in a typical car during a 160 km (100 mi) trip while traveling at 22 m/s (50 mi/h). The resistive force exerted by the air on the car is about 200 N. Thermal energy produced due to this resistive force during the trip is

One liter of gas releases about 3.25 X 10⁷ J of energy. So the gasoline energy that is equivalent to the resistive thermal energy produced during this trip is

In summary, you use about one-quarter gallon of gasoline to counter air resistance during the 160 km trip. Unfortunately, the car is only about 13% efficient (see Figure 13.9), where

Consequently, your useful output of 0.98 liters requires an energy input of (0.98 L)/0.13 = 7.5 L of gas to overcome this air

resistance. This is about half of the gasoline a typical car consumes when driving at a steady speed for 160 km. The other half is needed to overcome rolling resistance.

Assuming a 200-N drag force when traveling at 22 m/s through air of density 1.3 kg>m3, what is the closest value to the product CA in the drag force equation for the vehicle?

(a) 0.50 m² (b) 0.62 m² (c) 0.86 m²

(d) 1.1 m² (e) 1.5 m²