4. (i) A \( 30 kg \) iron block and a \( 40 kg \) copper block, both initially at \( 80^{\circ} C \), are dropped into a large lake at \( 15^{\circ} C \). Thermal equilibrium is established after a while as a result of heat transfer between the blocks and the lake water. Determine the total entropy change for this process. (ii) How much of the \( 100 kJ \) of thermal energy at \( 650 K \) can be converted to useful work? Assume the environment to be at \( 25^{\circ} C \). (Nov/Dec 2016) Refer: "P.K NAG Engineering Thermodynamics for similar problems"

Question

4. (i) A \( 30 kg \) iron block and a \( 40 kg \) copper block, both initially at \( 80^{\circ} C \), are dropped into a large lake at \( 15^{\circ} C \). Thermal equilibrium is established after a while as a result of heat transfer between the blocks and the lake water. Determine the total entropy change for this process. (ii) How much of the \( 100 kJ \) of thermal energy at \( 650 K \) can be converted to useful work? Assume the environment to be at \( 25^{\circ} C \). (Nov/Dec 2016) Refer: "P.K NAG Engineering Thermodynamics for similar problems"