Correct Answer - Option 4 : 83.33%
Concept:
Mechanical Efficiency:
It is the ratio of Brake power to the Indicated power.
\(\eta_m=\frac{B.P}{I.P}\)
Indicated power is the sum of brake power and frictional power.
Note: During half load, the brake power gets halved while the friction power remains same.
Calculation:
Given:
Brake power at full load = 100 kW, FP = 10 kW
\(\eta_m=\frac{B.P}{I.P}\)
\(\eta_m=\frac{B.P/2}{B.P/2\;+\;F.P}\)
\(\eta_m=\frac{50}{50\;+\;10}=83.33\;\%\)