Calculating Work & Displacement of a Piston w/ Fuel Energy

AI Thread Summary
The discussion focuses on calculating the work done by a piston in a combustion chamber based on the internal energy increase of fuel. The initial calculation of efficiency at 57.7% was deemed incorrect as it used the change in internal energy instead of work. Participants suggest referring to thermodynamic equations that relate internal energy, work, and heat. The correct approach involves identifying the appropriate equation for calculating work based on the given energy values. Clarification on the correct formulas is essential for accurate calculations.
nlsed
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Homework Statement


The Internal energy of fuel in a combustion chamber increases by 75J due to 130J of heating. How much work can be done by the piston? How far does the piston move while pushing with 5000N of force?

Homework Equations





The Attempt at a Solution


Since they gave us the info to find efficiency i divided 75J by 130J and got 57.7% eff. I plugged that into (e= w/QH) and got work = 75.01J and i plugged it into w=F *(delta x) and got .015m. I'm not sure if this is right, but the units seem to be correct.
 
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nlsed said:

The Attempt at a Solution


Since they gave us the info to find efficiency i divided 75J by 130J and got 57.7% eff. I plugged that into (e= w/QH) and got work = 75.01J and i plugged it into w=F *(delta x) and got .015m. I'm not sure if this is right, but the units seem to be correct.

Not quite.

As you said, efficiency is
e = w/QH​

However, you have used ΔU, not w, to calculate e=57.7%. So that's incorrect.

What is another equation that relates U, W, and Q? It should be in your textbook, early in the section or chapter on thermodynamics.
 
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