How much coal will it take to burn to melt an iron balvanka weighing 15 kg, the initial temperature is +20?

Initial data: m1 (weight of an iron bar) = 15 kg; t (initial temperature of the blank).

Constants: C (specific heat of iron) = 460 J / (kg * K); λ (specific heat of fusion of iron) = 2.7 * 10 ^ 5 J / kg; tmelt (melting point of iron) = 1539 ºС, q (specific heat of combustion of coal) = 2.7 * 10 ^ 7 J / kg.

Q1 + Q2 = Q3.

C * m1 * (tmelt – t) + λ * m1 = q * m2.

m2 = (C * m1 * (tmelt – t) + λ * m1) / q = (460 * 15 * (1539 – 20) + 2.7 * 10 ^ 5 * 15) / (2.7 * 10 ^ 7 ) = 0.538 kg = 538 g.