Internal energy of the gas in a gasoline engine

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Homework Help Overview

The discussion revolves around the internal energy changes in a gasoline engine, specifically focusing on the relationship between internal energy, work done, and heat transfer as described by the first law of thermodynamics.

Discussion Character

  • Conceptual clarification, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants explore the application of the first law of thermodynamics, questioning the signs associated with work done by the gas and its impact on heat transfer calculations.

Discussion Status

There is an ongoing examination of the correct application of the formula Q=U+W, with some participants suggesting different interpretations of the work done by the gas and its implications for calculating heat transfer. No consensus has been reached yet.

Contextual Notes

Participants are grappling with the signs of energy transfer and the definitions of work in the context of thermodynamics, which may affect their calculations. The original poster expresses confusion about the problem setup.

fletcher89
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I am so lost with this question. Can anyone help?

The internal energy of the gas in a gasoline
engine's cylinder decreases by 176:7 J.
If 67.0 J of work is done by the gas, how
much energy is transferred as heat? Answer
in units of J
 
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Use the first law of thermodynamic:
Q=U+W, where W is the work done by the gas
 
I did Q= 176.7 (change in energy) + 67 (amount of work done)

I got 243.7
What am I doing wrong
 
I think the mistake is here.
Q=U+W but since the work is fone by the gas the the +w might be deceiving.
W is positive if work is done on the gas.Since instead it is done by the gas it would imply you will have to add -67
Therefore the answer is 176.7-67=109.7
 

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