Термодинамика

$$\eta = 1 - \frac{Q_2}{Q_1} \implies Q_2 = Q_1 (1 - \eta) = 5 \times (1 - 0{,}3) = 3,5~\text{кДж}$$

$$\eta = 1 - \frac{Q_2}{Q_1} \implies Q_2 = Q_1 (1 - \eta) = 15 \times (1 - 0{,}2) = 12~\text{кДж}$$

$$\eta = 1 - \frac{T_2}{T_1} \implies T_1 = \frac{T_2}{1 - \eta} = \frac{300}{1 - 0{,}4} = 500~\text{К}$$

Переведём температуры в Кельвины: $$T_1 = 227 + 273 = 500~\text{К}, \quad T_2 = 27 + 273 = 300~\text{К}$$ $$\eta = 1 - \frac{T_2}{T_1} = 1 - \frac{300}{500} = 0{,}4 = 40\%$$

$$T_1 = 727 + 273 = 1000~\text{К}, \quad T_2 = 27 + 273 = 300~\text{К}$$ $$\eta = 1 - \frac{T_2}{T_1} = 1 - \frac{300}{1000} = 0{,}7 = 70\%$$