Question

A pulley system has four pulleys in all and is 60% efficient. Calculate (a) the mechanical advantage (b) the effort required to lift a load of 1200 N, (c) the resistance due to the movable parts and friction of the pulley system.

Answer 1

Velocity ratio = No. of pulleys = 4.

Knowing, \[ \eta = \frac{\mathrm{MA}}{\mathrm{VR}} \]

MA = η × VR

\[= \frac{60}{100} \times 4\]

= 2.4 

Also, \[ \frac{l}{E} = \mathrm{MA} \]

\[\text{E} = \frac{l}{\mathrm{MA}}\]

\[= \frac{1200\ \mathrm{N}}{2.4}\]

= 500 N

Knowing, \[ \mathrm{MA} = \mathrm{VR} - \frac{x}{E} \]

∴ x = E(VR − MA)

= 500(4 − 2.4)

= 800 N