Question

A man weighing 60kg lifts a body of mass 15 kg to the top of a building 10 m high in 3 minutes. His efficiency is

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

Answer 1

The correct option is A $20$

Input power is the power produced by man to reach the top of the building along with the body

Input power $=\frac{(M+m)gh}{t}$

Output power is the power required to take the body to top of the building

Output power $=\frac{mgh}{t}$

Effeciency $=\frac{\left(Outputpower\right)}{\left(Inputpower\right)}\times 100$

$=[\frac{\frac{mgh}{t}}{\frac{(M+m)gh}{t}}]\times 100$

$=[\frac{m}{(M+m)}]\times 100$

$=[\frac{15kg}{(15kg+60kg)}]\times 100$

$=20\text{\%}$