Q. An engineer claims to have made an engine delivering $10\ kW$ power with fuel consumption of $1\ g/s$. The calorific value of the fuel is $2\ kcal/g$. Is the claim of the engineer
A) Valid
B) Invalid
C) Depends on engine design
D) Depends of the load
Explanation
(b) Input energy $= \frac{1g}{s} \times \frac{2kcal}{g} = 2kcal/s$
Output energy $= 10\ kW = 10\ K\ J/S = \frac{10}{4.2}kcal/s$
$\Rightarrow \eta = \frac{output\ energy}{input\ energy} = \frac{10}{4.2 \times 2} > 1$, it is impossible
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.