how many kilometers per liter will a car obtain if its engine is 25% efficient and it encounters an average retarding force of 500N at highway speed? assume that the energy content of gasoline is 40Mj/liter

Answer 1

The work required to move the car 1 km will be 500 N x 1000 m = 5*10^5 J
At 25% efficiency, 20*10^5 J (=2 MJ) of chemical (fuel) energy will be required.

That will require 1/20 of a liter of gas, since you get 40 MJ of energy per lier.

The gas mileage is the reciprocal of that, 20 km per liter.

Answer 2

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