Question

In a block and tackle system, a load of 7.5 Kg is raised with an effort of 2.5 kgf. If there are three pulleys in the system, find its efficiency.

• A. 50%
• B. 75%
• C. 100%
• D. 125%

Answer 1

The correct option is C

100%

Given: load (W) = 7.5 Kg, effort (E) = 2.5 kgf and number of pulleys (n) = 3
Mechanical advantage $=\frac{W}{E}=\frac{7.5}{2.5}=3$
Velcity ratio = Number of pulleys = 3
$\therefore$ Efficiency $=\frac{Mechanicaladvantage}{Velocityratio}\times 100$
$=\frac{3}{3}\times 100=100\%$