Question

A man of mass 60 Kg lifts a 15 Kg mass to the top of a building of height 10 m in 5 minutes. H is efficiency is

• A. 10 %
• B. 20 %
• C. 30 %
• D. 40 %

Answer 1

The correct option is B 20 %

$\text{Given:-}$ Mass of the man $=60kg$,

mass $=15kg,$

height $=10m,$

Time $=30min$

$\text{Solution:-}$

The efficiency of a man is given by the ratio of his output power to input power.

Efficiency $=\eta =\frac{Outputpower}{Inputpower}\times 100$%

Power $=\frac{Workdone}{Time}$

We know,

$Workdone=Force\times displacement$

$Powe{r}_{out}=15\times 10\times 10=1500j$

$T=5\times 60=300sec$

$P_{out}=\frac{1500}{300}=5$

$\therefore P_{in}\to Power=60\times 10\times 10=6000j$

$P=\frac{W}{T}=\frac{6000}{300}=20$

Efficiency $=\eta =\frac{Outputpower}{Inputpower}\times 100$

$\eta =20$ %

$\text{Hence the correct option is B}$