Question:

A geyser heats water flowing at the rate of 3.0 liters per minute from 27°C to 77°C. If the geyser operates on a gas burner and if its heat of combustion is \( 4.0 \times 10^4 \text{ J g}^{-1} \), the rate of combustion of the fuel per minute is:

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When calculating fuel consumption, ensure consistent units for energy (Joules) and mass (grams or kilograms).
Updated On: Jun 9, 2026
  • \( 15.75 \times 10^{-3} \text{ g} \)
  • \( 15.75 \text{ g} \)
  • \( 252 \text{ g} \)
  • \( 252 \times 10^{-3} \text{ g} \)
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The Correct Option is B

Solution and Explanation

Concept: The heat required to raise the temperature of a mass of water is \( Q = mc\Delta T \). This heat must be supplied by the combustion of fuel: \( Q = m_{fuel} \times \text{Heat of Combustion} \).

Step 1: Calculate the heat required for the water.
Flow rate = 3.0 L/min = 3 kg/min (since density of water is 1 kg/L). Specific heat of water \( c = 4200 \text{ J kg}^{-1} \text{ K}^{-1} \). \( \Delta T = 77 - 27 = 50^\circ\text{C} = 50 \text{ K} \). $$ Q = 3 \text{ kg} \times 4200 \text{ J kg}^{-1} \text{ K}^{-1} \times 50 \text{ K} = 630,000 \text{ J/min} $$

Step 2: Determine the mass of fuel combusted.
$$ m_{fuel} = \frac{Q}{\text{Heat of Combustion}} = \frac{630,000}{4.0 \times 10^4} $$ $$ m_{fuel} = \frac{63}{4} = 15.75 \text{ g} $$ $$\boxed{15.75 \text{ g}}$$
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