The car covered 300 km at an average speed of 72 km / h. In this case, 70 liters of gasoline were consumed.

The car covered 300 km at an average speed of 72 km / h. In this case, 70 liters of gasoline were consumed. The efficiency of the car engine is 25%. What is the average power output of the engine during operation?

Data: S (vehicle path) = 300 km (300 * 10 ^ 3 m); Vav. (average speed) = 72 km / h (20 m / s); V (gasoline volume) = 70 l (0.07 m3); η (motor efficiency) = 25% (0.25).

Constants: ρb (gasoline density) = 710 kg / m3; q (beats heat of combustion of gasoline) = 4.6 * 107 J / kg.

We express the power of the car engine from the formula: η = Ap / Az = N * t / (q * m) = N * S / (q * ρb * V * Vav.), Whence N = η * q * ρb * V * Vav … / S.

Calculation: N = 0.25 * 4.6 * 10 ^ 7 * 710 * 0.07 * 20 / (300 * 10 ^ 3) = 38 103 W ≈ 38.1 kW.