The internal combustion engine performed useful work equal to 27.6 kJ

The internal combustion engine performed useful work equal to 27.6 kJ and consumed 3 liters of gasoline. What is the efficiency of the engine.

Ap = 27.6 MJ = 27.6 * 10 ^ 6 J.

V = 3 l = 3 * 10 ^ -3 m3.

q = 4.6 * 10 ^ 7 J / kg.

ρ = 710 kg / m3.

Efficiency -?

For an internal combustion engine of a car, the efficiency is expressed by the formula: efficiency = Ap * 100% / Az, where Ap is the work of the engine, which benefits, Az is the expended work of the internal combustion engine.

The amount of thermal energy Q, which is released during the combustion of gasoline, turns into the expended work Az. The amount of heat Q is expressed by the formula: Q = q * m, where q is the specific heat of combustion of gasoline, m is the mass of gasoline that has burned.

We express the mass of the burnt gasoline by the formula: m = ρ * V.

We take the density ρ and the specific heat of combustion of gasoline q from the corresponding tables: q = 4.6 * 10 ^ 7 J / kg, ρ = 710 kg / m3.

Efficiency = Ap * 100% / q * ρ * V.

Efficiency = 27.6 * 10 ^ 6 J * 100% / 4.6 * 10 ^ 7 J / kg * 710 kg / m3 * 3 * 10 ^ -3 m3 = 28%.

Answer: the internal combustion engine of a car has an efficiency of 28%.