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Homework Statement
1. A heat engine operating between 200°C and 80.0°C achieves 20.0% of the maximum possible efficiency. What energy input will enable the engine to perform 10.0 kJ of work?
Homework Equations
e =1- Tc/Th
W=e*Qh
The Attempt at a Solution
I got the answer but I don't understand why Qh is negative and could you also explain why work is negative too? I'm guessing since the work is the output its negative? But why would the Qh be negative to isn't it the input? Also could you tell/explain when W, Qh and Qc are positive and negative? Thank you.