The car on the way of 100 km consumed gasoline weighing 6.9 kg, while doing work equal to 12.7 MJ. What is the efficiency of the car?

S = 100 km = 100000 m.

m = 6.9 kg.

Ap = 12.7 MJ = 12.7 * 10 ^ 6 J.

λ = 4.6 * 10 ^ 7 J / kg.

Efficiency -?

The efficiency factor of the engine efficiency shows what part of the spent work Az, expressed as a percentage, goes into useful work Ap: Efficiency = Ap * 100% / Az.

When gasoline is burned in the engine, the amount of heat Q is released, which turns into the expended work: Az = Q.

Q = λ * m, where λ is the specific heat of combustion of gasoline, m is the mass of gasoline that has burned.

Efficiency = Ap * 100% / λ * m.

Efficiency = 12.7 * 10 ^ 6 J * 100% / 4.6 * 10 ^ 7 J / kg * 6.9 kg = 4%.

Answer: the car engine has an efficiency of 4%.