How much natural gas needs to be burned to perform useful work 220 kJ, if the engine efficiency is 25%.

To find the mass of burnt natural gas, we will use the formula: η = An / Q = An / (qg * m), whence we express: m = An / (η * qg).

Values of variables and constants: Ap – the required useful work (Ap = 220 kJ = 220 * 10 ^ 3 J); η – efficiency of the used motor (η = 25% = 0.25); qg – specific heat of combustion of natural gas (qg = 4.4 * 10 ^ 7 J / kg).

Calculation: m = Ap / (η * qg) = 220 * 10 ^ 3 / (0.25 * 4.4 * 10 ^ 7) = 0.02 kg or 20 g.

Answer: It is necessary to burn 20 g of natural gas.



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