Q. An engineer claims to have made an engine delivering 10 KW power with fuel consumption of 1 $gs^{- 1}.$ The calorific value of fuel is $2kcalg^{- 1}$. This claim is
A) Valid
B) Invalid
C) Dependent o engine design
D) Dependent on load
Explanation
(b) Efficiency, $\eta = \frac{output\ power}{consuming\ power} \times 100\%$
$Here\ ,\ P_{output} = 10kW$
$P_{input} = 2 \times 10^{3}calg^{- 1} \times gs^{- 1}$
$= 2 \times 10^{3}cals^{- 1}$
$= 2 \times 10^{3} \times 4.2Js^{- 1}$
$8.4kW$
As, $P_{output} > P_{input}$, hence it is never possible.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.