Calculation of work done by/on engine

In summary, during the working cycle of an engine, 200kJ/kg of heat was transferred out of the system and the internal energy decreased by 300kJ/kg of working fluid. Using the equation W = Q - E, we can calculate that the work done was 100kJ, and based on energy conservation, this indicates that the work was done by the engine.
  • #1
aks2708
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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 teh 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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  • #2
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?
 

1. How is work done by an engine calculated?

The work done by an engine can be calculated by multiplying the force exerted by the engine on an object by the distance the object moves in the direction of the force.

2. What is the unit of measurement for work done?

The unit of measurement for work done is joule (J) in the International System of Units (SI). In some cases, other units such as foot-pound (ft-lb) or calorie (cal) may also be used.

3. How is work done by an engine different from power?

Work done and power are two different concepts. Work done is the measure of energy transfer that occurs when a force is applied to an object and causes it to move a certain distance, while power is the rate at which work is done, or the amount of work done per unit of time.

4. Can the work done by an engine be negative?

Yes, the work done by an engine can be negative if the force and direction of motion are in opposite directions. This means that the engine is doing work against the motion of the object, such as in the case of braking.

5. How does the efficiency of an engine affect the work done?

The efficiency of an engine is a measure of how well it converts energy into work. A more efficient engine will produce a greater amount of work for a given amount of energy input. Therefore, a more efficient engine will have a higher work output compared to a less efficient engine.

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