Question

A car engine operates with a thermal efficiency of 35%. Assume the air conditioner has a COP of 3 working as a refrigerator cooling the inside, using engine shaft work to drive it. How much extra fuel energy should be spent to remove 1 kJ from the inside ?

• A. 1.95 kJ
• B. 0.95 kJ
• C. 0.35 kJ
• D. 0.105 kJ

Answer 1

The correct option is B 0.95 kJ


For air conditioner,

$(COP{)}_R=3=\frac{RE}{W_{in}}$

$3=\frac{1}{W}$

$W=\frac{1}{3}$

For engine,

${\eta }_c=\frac{W}{Q_{fuel}}$

$0.35=\frac{\frac{1}{3}}{Q_{fuel}}$

$Q_{fuel}=0.95kJ$