Determine the mass of water, if 100 g of gasoline is required to heat it from 20 degrees to 80 degrees. Efficiency 60%.

η = (Q1 / Q2) * 100%, η (efficiency) = 60% = 0.6.

Q1 – water heating: Q1 = С * m1 * (tк – tн), where С is the specific heat capacity of water (С = 4200 J / (kg * K)), m1 is the required mass of water, tк = 80 ºС, tn = 20 ºС.

Q2 is the combustion of gasoline: Q2 = q * m2, where q is the specific heat of combustion of gasoline (q = 4.6 * 10 ^ 7 J / kg), m2 is the mass of gasoline spent (m = 100 g = 0.1 kg).

С * m1 * (tк – tн) = η * q * m2.

m1 = η * q * m2 / (С * (tк – tн)) = 0.6 * 4.6 * 10 ^ 7 * 0.1 / (4200 * (80 – 20)) = 10.95 kg.