Question

A bucket of water needs to be lifted up through a single movable pulley system by a boy who can apply an effort of up to $100\text{N}$. How much weight of the bucket can he lift up if the pulley system has an efficiency of $75\%$?

• A. $50\text{N}$
• B. $200\text{N}$
• C. $100\text{N}$
• D. $150\text{N}$

Answer 1

The correct option is D $150\text{N}$

Given-
Maximum effort available, $E=100\text{N}$
Efficiency, $\eta =75\%$
Since, it is a single movable pulley system,
Velocity ratio, $\text{VR}=2$
We know that,
$\eta =\frac{\text{MA}}{\text{VR}}\times 100$
$75=\frac{\text{MA}}{2}\times 100$
$⟹\text{MA}=1.5$
And, $\text{MA}=\frac{\text{Load}}{\text{Effort}}$
$1.5=\frac{\text{Load}}{100}$ $⟹$ Load $=150\text{N}$