Temperature in a Carnot heat engine

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SUMMARY

The discussion centers on calculating the temperature of the hot reservoir in a Carnot heat engine. The engine operates with 95 cycles, lifting a 10 kg mass to a height of 11 m, while exhausting 14 J of heat per cycle to a cold reservoir at 0°C. The correct calculation for the hot reservoir temperature (Th) is derived using the formula Qh = W + Qc, resulting in Th = 494 K (221°C). This conclusion corrects an initial miscalculation that yielded an implausibly high temperature.

PREREQUISITES
  • Understanding of Carnot heat engine principles
  • Familiarity with thermodynamic equations, specifically η = 1 - (Tc/Th)
  • Basic knowledge of work (W) and heat (Q) calculations
  • Ability to manipulate equations involving multiple variables
NEXT STEPS
  • Study the principles of Carnot efficiency and its implications in thermodynamics
  • Learn about the relationship between work and heat in thermodynamic cycles
  • Explore advanced thermodynamic equations and their applications
  • Investigate real-world applications of Carnot engines in energy systems
USEFUL FOR

Students studying thermodynamics, engineers working with heat engines, and anyone interested in the principles of energy conversion and efficiency in mechanical systems.

EightBells
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Homework Statement


A Carnot heat engine takes 95 cycles to lift a 10 kg. mass a height of 11 m . The engine exhausts 14 J of heat per cycle to a cold reservoir at 0∘C.

What is the temperature of the hot reservoir?

Homework Equations


η=1-(Tc/Th)=W/Qh

The Attempt at a Solution


I've tried: (Energy to lift mass)/(number of cycles)=W, so (mgh)/95=((10kg)(9.8m/s^2)(11m))/95= W=11.35 J/cycle
∴ 1-(Tc/Th)=11.35/14, so Tc/Th=1-(11.35/14), Th=Tc/(1-(11.35/14))=273 K/(1-(11.35/14))=1440 K=1170°C

This is an incorrect answer, and logically it seems too high.

I also considered where the 14 J/cycle exhausted to the cold reservoir is the work out, but then I don't know how to calculate Qh so that I'd only have one variable in the equation listed under 'Relevant Equations'.
 
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The problem statement says 14 J is the heat exhausted to the cold reservoir, so it's ##Q_\text{C}##, not ##Q_\text{H}##. You calculated ##W## correctly. How do you get ##Q_\text{H}## from ##Q_\text{C}## and ##W##?
 
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vela said:
The problem statement says 14 J is the heat exhausted to the cold reservoir, so it's ##Q_\text{C}##, not ##Q_\text{H}##. You calculated ##W## correctly. How do you get ##Q_\text{H}## from ##Q_\text{C}## and ##W##?

Qh=W+Qc=11.35+14=25.35 J/cycle

Plug that into W/Qh=1-(Tc/Th) and Th=494 K=221°CThat's the correct answer, thanks so much!
 

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