A copper block of mass $2 kg$ is heated to a temperature of ${500}^o C$ and then placed in a large block of ice at $0^{o}C$. What is the maximum amount of ice that can melt? The specific heat of copper is $400 {\mathrm{JKg}}^{-1}{}^{\mathrm{o}}\mathrm{C}^{-1}$and latent heat of fusion of water is $3.5\times {10}^5 JK{g}^{-1}$.

Heat energy in copper block$=2\times 400\times 500=4\times {10}^{5}J$. The amount of ice that melts will be maximum if the entire heat energy of the copper block is used up in melting ice. Now, $3.5\times {10}^5 J$ of heat energy is needed to melt $1 kg$ of ice into water. Therefore, the amount of ice melted by $4\times {10}^5 J$ of heat energy is

                $\frac{4\times {10}^5\mathrm{J}}{3.5\times {10}^5\mathrm{J} {\mathrm{kg}}^{-1}}=\frac{8}{7}\mathrm{kg}$