Question

A car engine produces an average of 25 kW of power in a period of 10-min during which 1.25 kg of gasoline is consumed. If the heating value of gasoline is 43,000 kJ/kg, the efficiency of this engine during this operation is:

A. 24%B. 28%C. 32%D. 36%

Answer 1

Answer:B

Explanation:

Given

Power Produced $P=25\ kW$

time $t=10\ min$

Gasoline consumed $m=1.25\ kg$

Heat capacity of Gasoline $C=43,000\ kJ/kg$

Heat Provided by Gasoline $Q_s=m\times C$

$Q_s=1.25\times 43000=53,750\ kJ$

Energy used in Producing Power is $W=25\times 10\times 60=15,000\ kJ$

Efficiency of an engine is

$\eta =\frac{Work}{Energy\ Supplied}$

$\eta =\frac{15000}{53750}=0.2790$

$\eta =27.90\approx 28\ \%$