GATE 2020 ME (ME1) – Question 62
One kg of ideal air at 127°C expands reversibly at constant pressure until its volume doubles. Gas constant is 287 J/(kg·K). Find magnitude of work transfer (kJ), to two decimals.
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Correct answer: 114.6 to 115
Explanation
At fixed pressure, volume is proportional to absolute temperature. Initial T=400 K, final T=800 K. Boundary work is mR(T2−T1)=1×287×400=114800 J=**114.80 kJ**. Doubling Celsius temperature would be incorrect.