240 kg of water was heated to a temperature of 60 degrees by burning coal. How much coal was burned if half of the energy obtained as a result of its combustion was used to heat the water? The initial temperature of the ox is 10 degrees.
Data: m (mass of water) = 240 kg; t (temperature to which the water was heated) = 60 ºС; η (the percentage of energy from the combustion of coal, which was used to heat water) = 50%; t0 (initial temperature) = 10 ºС.
Const: q (heat of combustion of coal) = 2.7 * 10 ^ 7 J / kg; Cw (heat capacity of water) = 4200 J / (kg * K).
We express the mass of burnt coal from the formula: η = Cw * m * (t – t0) / (q * m), whence m = Cw * m * (t – t0) / (q * η).
Calculation: m = 4200 * 240 * (60 – 10) / (2.7 * 10 ^ 7 * 0.5) = 3.73 kg.
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