What mass of coal must be burned to heat 0.3 tons of brick from 5 degrees to 95 degrees, if 70% of the heat

What mass of coal must be burned to heat 0.3 tons of brick from 5 degrees to 95 degrees, if 70% of the heat is used to heat the brick? 800 J / kg * C, q 42 * 10 in 6 J?

Given: m1 (mass of the heated brick) = 0.3 t (in SI m1 = 300 kg); t0 (initial brick temperature) = 5 ºС; t (final temperature) = 95 ºС; η (percentage of heat used to heat the brick) = 70% (0.7).

Constants: according to the condition CK (specific heat capacity of a brick) = 800 J / (kg * ºС); q (specific heat of combustion of coal) = 42 * 106 J / kg.

We express the mass of coal from the formula: η = Cк * m1 * (t – t0) / (q * m2); m2 = Cк * m1 * (t – t0) / (η * q).

Calculation: m2 = 800 * 300 * (95 – 5) / (0.7 * 42 * 106) = 0.735 kg (735 g).