Solution to 1996 Problem 14

Assuming that the specific heat is constant during the entire process, the final temperature of the two blocks must be 50 \;^{\circ}\mathrm{C} in order for energy to be conserved. The amount of energy required to increase the temperature of the block initially at 0 \;^{\circ}\mathrm{C} to 50 \;^{\circ}\mathrm{C} is
\begin{align*}\frac{0.1 \mbox{ kcal}}{\mbox{ kg} \;^{\circ}\mathrm{C}}\cdot 50 \;^{\circ}\mathrm{C} \cdot 1 \mbox{ kg} = 5 \m...
The blocks are enclosed in a perfectly insulating container, so this must also be the amount of energy transferred between the two blocks. Therefore, answer (D) is correct.

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