Question

An engineer claims to have made an engine delivering $10kW$ power with fuel consumption of $1g/s$. The calorific value of fuel is $2kcal/g$. This claim is:

• A. Valid
• B. Invalid
• C. Dependent on engine design
• D. Dependent on load

Answer 1

The correct option is B Invalid

Efficiency of engine is given by
$\eta =\frac{\text{output power}}{\text{input power}}\times 100$ %
Here, $P_{output}=10kW$
$P_{input}=2\times {10}^3/g\times 1g/s$
$=2\times {10}^{3}cal/s$
$=2\times {10}^3\times 4.2J/s$
$=8.4kW$
As, $P_{output}>P_{input}$, hence it is never possible.