The energy input to an engine is 60 J, and the work it performs is 15 J. What fraction of the energy input is expelled to the cold reservoir?
Correct answer: B. 75%
- A. 0.25
- B. 75%
- C. 1
- D. Impossible to determine
Explanation
If work is 15J out of 60J, then 45J is expelled to the cold reservoir, which is 45/60×100, thus 75%.
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About First Law of Thermodynamics
The first law relates heat supplied, work done and the change in internal energy through energy conservation. Problems use sign conventions and apply the law to isothermal, adiabatic, isobaric and isochoric processes. Internal energy is a state function, while heat and work depend on the path followed.
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