Question

A man of weight $60kgwt$ takes a body of mass $15kg$ at a height $10m$ on a building in $3minutes$. The efficiency of man is

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

Answer 1

The correct option is B

$20\%$

Step 1: Given data:

According to the question, we have given

A man of weight $60kgwt$ Takes a body of mass $15kg$at a height $10m$ on a building in $3minutes$.

Step 2: Calculate the efficiency of man

Work done in the initial state,

$$\begin{gathered} \Rightarrow Workdone=mgh \\ \Rightarrow W=15\times 10\times 10=1500 \\ \Rightarrow W=1500J \end{gathered}$$

Work done in the final state,

$$\begin{gathered} \Rightarrow Workdone=mgh \\ \Rightarrow W=\left(M+m\right)gh \\ \Rightarrow W=\left(60+15\right)\times 10\times 10 \\ \Rightarrow W=7500J \end{gathered}$$

The efficiency of man is

$$\begin{gathered} \Rightarrow \frac{1500}{7500}\times 100 \\ \Rightarrow \frac{1500}{75} \\ \Rightarrow 20\% \end{gathered}$$

Hence, option (B) is the correct answer.