Question

The figure shows a diagram of a system of four pulleys. The upper two pulleys are fixed and the lower two are movable. What are the mechanical advantage and velocity ratio of the system?

• A. M.A. = 5
• B. M.A = 2
• C. V.R = 4
• D. V.R = 2

Answer 1

The correct option is C

V.R = 4

Let the load attached with the pulley be W, E be the effort applied at the free end and the weight of lower block is neglected.
Then in equilibrium, W = nT(n = number of pulleys) and E = T.
$\therefore$ Mechanical advantage $=\frac{W}{E}=\frac{nT}{T}$
$n=4$

Let the load moves up through a distance d, then the effort moves through distance nd because each string is loosened by length d.
$\therefore$ Velocity ratio $=\frac{nd}{d}=\frac{4d}{d}=4$