A geyser, operating on LPG (liquefied petroleum gas) heats water flowing at the rate of 3.0 litres per minutes, from 27°C to 77°C. If the heat of combustion of LPG is 40,000 J/g, how much fuel, in g,

Question

A geyser, operating on LPG (liquefied petroleum gas) heats water flowing at the rate of 3.0 litres per minutes, from 27°C to 77°C. If the heat of combustion of LPG is 40,000 J/g, how much fuel, in g, is consumed per minute? (Specific heat capacity of water is 4200 J/kg-K)

Prashant Kotian · Accepted Answer

Correct answer: C. Mass of water heated per minute: m = 3.0 kg (since density of water is 1 kg/L). Temperature difference: δ T = 77 - 27 = 50 K. Heat required per minute: q = m * s * δ T = 3.0 kg * 4200 J/(kg K) * 50 K = 630,000 J. Heat of combustion of LPG = 40,000 J/g. Mass of fuel consumed per minute: m_fuel = q / heat_of_combustion = 630,000 J / 40,000 J/g = 15.75 g.

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