Define one calorie.

Find the final temperature of a copper rod. Whose area of cross section changes from $10 {\mathrm{m}}^2$ to $11 {\mathrm{m}}^2$ due to heating. The copper rod is initially kept at $90 \mathrm{K}$. (Coefficient of superficial expansion is $0.0021 {\mathrm{K}}^{-1}$)