A car's engine is 20% efficient. When cruising, the car encounters an average retarding force of 1000 N. If the energy content of fuel is 40 megajoules per liter, how many kilometers per liter does the car achieve?

Question

Quizplus · Accepted Answer

The car's engine is 20% efficient, so only 20% of the fuel's energy is used for work. The energy content of the fuel is 40 MJ/L, so the useful energy is 0.2 * 40 MJ = 8 MJ/L. The work done against the retarding force is force * distance. To find the distance per liter, set 8 MJ = 1000 N * distance, solving gives distance = 8000 m = 8 km. Thus, the car achieves 8 km per liter.

A Car's Engine Is 20% Efficient