Question

An effort of $240\text{N}$ overcome a useful load $1000\text{N}$ when applied to a block and system of pulleys; such that the weight of movable block and friction is $220\text{N}$. What is the efficiency of the system?

• A. $81.2\%$
• B. $82.5\%$
• C. $83.4\%$
• D. $84\%$

Answer 1

The correct option is C $83.4\%$

Given:
Load = $1000\text{N}$
Effort = $240\text{N}$ , and
Weight of the block and friction = $200\text{N}$

Mechanical advantage $=\frac{\text{Load}}{\text{Effort}}=\frac{1000}{240}=4.17$

Velocity Ratio = Ideal mechanical advantage

$=\frac{\text{Resistance overcome}}{\text{Effort}}$

$=\frac{\text{Useful load other force}}{\text{Effort}}$

$=\frac{1000+200}{240}=\frac{1200}{240}=5$

Efficiency $=\frac{\text{M.A.}}{\text{V.R}}\times 100=\frac{4.17}{5}\times 100=83.4\%$