Question

An effort of 240 N overcome a useful load 1000 N when applied to a block and system of pulleys, such that the weight movable block and friction is 200 N.
Calculate the efficiency of the system (to the nearest integer).

• A. 83%
• B. 89%
• C. 91%
• D. 79%

Answer 1

The correct option is A

83%

Given: Load = 1000 N, effort = 240 N and friction = 200 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 $=\frac{\text{MA}}{\text{VR}}\times 100=\frac{4.16}{5}\times 100=83.2\%\approx 83$