Question

a) What is single movable pulley?
b) What is its mechanical advantage in an ideal case?

c) If the effort moves by a distance x upwards, by what height is the load raised?
d) Give two reasons why its efficiency is not $100\%$ in practice.

Answer 1

a)

1. A pulley is a mechanical device that can be used to lift heavy objects more easily. Pulleys consist of a wheel that rotates on an axle—which is a rod through the centre of the wheel—and a rope, cable, or chain
2. Single movable pulley: A single movable pulley is a pulley that is free to move up and down, and is attached to a ceiling or other object as shown below:

b)

1. The mechanical advantage in the ideal case is 2 as the load can be lifted by applying an effort equal to half the load.
2. A single, movable pulley acts as a force multiplier.

c)

1. Load L is attached to the movable pulley. A rope is fixed at a point in the ceiling that passes through the moveable pulley.
2. In order to lift the effort E by $x$ meters, the load L needs to travel the distance of $x/2$ meters. (The entire rope needs to be pulled by E for a distance of $x$)
3. Velocity Ratio equals $=\frac{dis\tan cetravelledbyEffort}{dis\tan cetravelledbyload}$
4. $Velocityratio=\frac{x}{\left({\displaystyle \frac{x}{2}}\right)}$
5. Therefore, $Velocityratio=2$
6. Therefore, $effortmovesbydis\tan cexupwards,theheightthatloadisraised=\frac{x}{2}$

d)

The efficiency of a single movable pulley system is not $100\%$ because of the following reasons:

1. There is friction in the pulley bearings or at the axle.
2. The weight of the pulley and string is not zero.