Calculation of work done by/on engine

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SUMMARY

The calculation of work done by or on an engine during its working cycle is determined using the equation W = Q - E. In this scenario, the heat transferred out of the system is -200 kJ/kg, and the decrease in internal energy is -300 kJ/kg. The resulting work done is calculated as W = -200 - (-300) = 100 kJ/kg, indicating that the work is done by the engine. This conclusion is based on the principles of energy conservation, where the system loses energy through both heat and work.

PREREQUISITES
  • Understanding of thermodynamics principles, specifically the first law of thermodynamics.
  • Familiarity with energy transfer concepts, including heat and work.
  • Knowledge of internal energy and its implications in thermodynamic systems.
  • Ability to manipulate equations involving energy conservation.
NEXT STEPS
  • Study the first law of thermodynamics in detail to grasp energy conservation principles.
  • Learn about different types of thermodynamic cycles and their applications in engines.
  • Explore the implications of heat transfer in various thermodynamic processes.
  • Investigate real-world examples of work done by engines in practical applications.
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Students studying thermodynamics, engineers working with engine design, and anyone interested in understanding energy transfer in mechanical systems.

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Homework Statement



During the working cycle of an engine, the heat transferred out of the system was 200kj/kg of working fluid. The internal energy also decreased by 300kj/kg of working fluid. find the work done and state whether it is work done on the engine or by the engine.

Homework Equations



W = Q- E

The Attempt at a Solution


W = Q-E

Since heat transferred out so Q = -200
Decrease in internal energy E = -300

Work done = -200-(-300) = 100.

Please correct me if i am wrong. I am not sure if it is work done by the engine or on the engine
 
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Think of it in terms of energy conservation. Considering 1kg of fluid as a "system", the system went through a cycle and in the process lost 300kJ of energy. All those 300kJ had to be transferred as either heat or work. Now, if you measured 200kJ of heat coming out, what can you say about the energy that was transferred in the form of work (i.e. the rest of it)? Did the work take extra energy out of the system, or did it add energy back into the system?
 

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