There can be two type of heat energy: sensible heat and latent heat. Sensible heat is the heat added or remove to change the temperature of the substance. Latent heat is the heat added or removed at constant temperature when phase change occurs. In this case, we compute the sensible heat. Its equation is:
Heat energy = mCpΔT
where Cp is the specific heat of a specific substance. For iron, Cp = 0.444 J/g·°C. For copper, Cp = 0.385 J/g·°C.
Thus, the solutions and answers are as follows:
1.) 18,000 J = (1.8 kg)(444 J/kg·°C)(T - 27°C)
T = 49.52°C
2.) 18,000 J = (850 g)(0.385 J/g·°C)(T - 23°C)
T = 78°C