Question

To reduce the drag coefficient and thus to improve the fuel efficiency of cars, the design of side rearview mirrors has changed drastically in recent decades from a simple circular plate to a streamlined shape. Determine the amount of fuel and money saved per year as a result of replacing a 13-cm-diameter flat mirror by one with a hemispherical back, as shown in the figure. Assume the car is driven 21,200 km a year at an average speed of 80 km/h. Take the density and price of gasoline to be 0.75 kg/L and $0.90/L respectively, the heating value of gasoline to be 44,000 kJ/kg: and the overall efficiency of the drive train to be 30 percent. The drag coefficient Co is 1.1 for a circular disk and 0.40 for a hemispherical body. Flat mirror 80kmh → D- 13 cm Rounded mirror 80 km/h D 13 cm The amount of fuel saved by replacing the flat mirror by a hemispherical one is The cost reduction due to the replacement of the flat mirror by a hemispherical one is L. per year.

Answer 1

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