Question

A block and tackle system of pulleys has a velocity ratio of 4.

1. Draw a labelled diagram.
2. What is the value of MA for an ideal pulley system?
3. What will be its velocity ratio if the weight of the movable blocks is doubled?

Answer 1

i. 

ii. For any ideal machine, efficiency (η) is perfect at 100% (η = 1).

MA = Velocity Ratio (VR) × Efficiency (η)

= 4 × 1

= 4

iii. The Velocity Ratio (VR) depends purely on the geometry of the system.

It is the ratio of distance moved by effort to distance moved by load.

It equals the number of rope strands supporting the load.

Changing the weight changes mechanical advantage, but not the geometry.

The velocity ratio remains 4.