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An iron block of unknown mass at 858C is dropped into an
Chapter 8, Problem 842(choose chapter or problem)
An iron block of unknown mass at 858C is dropped into an insulated tank that contains 100 L of water at 208C. At the same time, a paddle wheel driven by a 200-W motor is activated to stir the water. It is observed that thermal equilibrium is established after 20 min with a final temperature of 248C. Assuming the surroundings to be at 208C, determine (a) the mass of the iron block and (b) the exergy destroyed during this process.
Questions & Answers
QUESTION:
An iron block of unknown mass at 858C is dropped into an insulated tank that contains 100 L of water at 208C. At the same time, a paddle wheel driven by a 200-W motor is activated to stir the water. It is observed that thermal equilibrium is established after 20 min with a final temperature of 248C. Assuming the surroundings to be at 208C, determine (a) the mass of the iron block and (b) the exergy destroyed during this process.
ANSWER:Step 1 of 6
A hot iron block is dropped into water in an insulated tank that is stirred by a paddle-wheel. The mass of the iron block and the exergy destroyed during this process are to be determined.
Assumptions are
1. Both the water and the iron block are incompressible substances with constant specific heats at room temperature.
2. The system is stationary and thus the kinetic and potential energies are negligible.
3. The tank is wellinsulated and thus there is no heat transfer.
The density and specific heat of water at 
