Determine the mass of a copper bar if 42kJ of energy is needed to melt it.

The amount of heat required to melt a copper bar taken at the melting temperature:

Q = λ * m, where Q is the consumed amount of heat (Q = 42 kJ = 42000 J), λ is the specific heat of fusion of copper (λ = 2.1 * 10 ^ 5 J / kg), m is the mass of a copper bar (kg ).

Let us express and calculate the mass of a copper bar:

m = Q / λ = 42000 / (2.1 * 10 ^ 5) = 0.2 kg = 200 g.

Answer: The mass of a copper bar is 200 g.