Question

Diagram shows a single movable pulley system.

1. Mark the direction of force due to tension.
2. What is the purpose of the fixed pulley?
3. If T is the tension in newtons, what is the relation between T and E?
4. Calculate VR of the system.
5. Assuming efficiency is 100%, what is the mechanical advantage?
6. Calculate the effort E.

Answer 1

(a)

(b) The fixed pulley changes the direction of the effort. Without it, the effort would have to be applied upward. With it, the effort can be applied downward, which is more convenient. It does not add any mechanical advantage, so the MA of the system stays 2.

(c) The tension in the rope is equal in magnitude to the effort: T = E.

(d) The movable pulley is supported by two sections of rope. Therefore, the effort moves twice as far as the load moves. 

\[ \mathrm{VR} = \frac{\text{distance moved by effort}}{\text{distance moved by load}} = 2 \]

(e) Efficiency = MA ÷ VR. With 100% efficiency, MA = VR = 2.

(f) \[ \mathrm{MA} = \frac{\text{Load}}{\text{Effort}}\]

\[\text{Effort} = \frac{\text{Load}}{\mathrm{MA}}\]

\[= \frac{100\ \mathrm{N}}{2} \]

= 50 N