Question

A boy uses a single fixed pulley to lift a load of 50 kgf to some height. Another boy uses a single movable pulley to lift the same load to the same height. Compare the effort applied by them. Give a reason to support your answer.

Answer 1

Mechanical Advantage$\left(\mathrm{MA}\right)$: It is the ratio of the load$\left(\mathrm{L}\right)$ to the effort$\left(\mathrm{E}\right)$.

$\mathrm{MA}=\frac{\mathrm{L}}{\mathrm{E}}$

The weight of load given is$=50\mathrm{kgf}$

Case I

In the case of the first boy uses a single fixed pulley ${\mathrm{MA}}_1=1$

$\begin{array}{rcl}{\mathrm{MA}}_1& =& \frac{50}{{\mathrm{E}}_1}\\ 1& =& \frac{50}{{\mathrm{E}}_1}\\ {\mathrm{E}}_1& =& 50\mathrm{N}\end{array}$

Case II

In the case of the second boy uses a movable pulley to lift the same load ${\mathrm{MA}}_2=2$

$\begin{array}{rcl}2& =& \frac{50}{{\mathrm{E}}_2}\\ {\mathrm{E}}_2& =& 25\mathrm{N}\end{array}$

Thus, the ratio of effort applied is,

$$\begin{gathered} \frac{E_1}{E_2}=\frac{50}{25} \\ \frac{E_1}{E_2}=\frac{2}{1} \end{gathered}$$

Thus, the ratio of effort applied is $2:1$.