Question

Diagram alongside shows a pulley system when a load of 30 kgf is attached to a movable block.

1. What is the velocity ratio of pulley system?
2. What is the mechanical advantage of pulley system assuming it is ideal?
3. What is the magnitude of effort applied?
4. If the pulley system is not ideal and is 60% efficient, what is the effort required?

Answer 1

(a) Velocity ratio = No. of supporting segments of the string = 3

(b) Assuming pulley system as ideal.

MA = Velocity ratio = 3

(c) \[\mathrm{MA} = \frac{l}{E} \]

\[ \therefore\ 3 = \frac{30\ \mathrm{kgf}}{E}\]

E = 10 kgf

(d) When efficiency of pulley is 60%.

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

MA = η × VR

\[\frac{l}{E} = \eta \times \mathrm{VR} \]

\[\frac{30\ \mathrm{kgf}}{\mathrm{E}} = \frac{60}{100} \times 3 \]

\[ \therefore\ E = \frac{30\ \mathrm{kgf} \times 100}{3 \times 80}\]

\[= \frac{50}{3}\ \mathrm{kgf}\]

= 16.67 kgf