Question:
In a thermodynamic process, a gas releases 20 J of heat and 10 J of work is done on the gas. If initial internal energy was 40 J, the final internal energy is:
In a thermodynamic process, a gas releases 20 J of heat and 10 J of work is done on the gas. If initial internal energy was 40 J, the final internal energy is:
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Remember sign conventions: $Q > 0$ for heat added, $W > 0$ for work done by gas.
Updated On: Jun 10, 2026
- 30 J
- 20 J
- 60 J
- 40 J
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The Correct Option is A
Solution and Explanation
Step 1: Concept
First Law of Thermodynamics: $\Delta U = Q - W$.
Step 2: Analysis
Heat released $Q = -20 J$. Work done *on* the gas $W = -10 J$. $\Delta U = (-20) - (-10) = -20 + 10 = -10 J$. $U_f - U_i = -10 J \implies U_f = 40 - 10 = 30 J$.
Step 3: Conclusion
Final internal energy is 30 J.
Final Answer: (A)
First Law of Thermodynamics: $\Delta U = Q - W$.
Step 2: Analysis
Heat released $Q = -20 J$. Work done *on* the gas $W = -10 J$. $\Delta U = (-20) - (-10) = -20 + 10 = -10 J$. $U_f - U_i = -10 J \implies U_f = 40 - 10 = 30 J$.
Step 3: Conclusion
Final internal energy is 30 J.
Final Answer: (A)
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