Solving Carnot Heat Problem: 1637.8BTU Answered

[Windseaker]

Homework Statement

Problem: A heat engine is connected to a 300watt motor. If we power the motor for 4hrs and heat engine is 40% efficient,how much heat is extracted from heat source in?

Homework Equations

Given: Q= heat QC=waste heat QH=W+QC and Power=E/t or Work/t

The Attempt at a Solution

This is a diagram equation of heat.
QH-----l----->QC
l
l
V
300w

300W(3.412btu/1W)= 1023.6btu (4hr) = 4094.4 btuh
----- 4094.4btu(40%)=1637.8btuh

 

[ehild]

The engine uses more heat energy than the work it yields: the work is 40 % of the heat: W=0.4*Q.

Do you really use btu units for heat instead of joule?

ehild

 

[Windseaker]

So, are you saying that time is not used here (4hrs)? its just the starting heat loss.

yes btu, this is more about residential usage in US.