WAEC Physics 2022 Paper

Concept:For a wheel and axle, the velocity ratio is the ratio of their radii.Efficiency compares the mechanical advantage with the velocity ratio.Explanation:Given radius ratio $= 5:1$, so velocity ratio $\mathrm{VR} = 5$.Load mass $= 20\,\text{kg}$.Therefore, load weight $W = mg = 20 \times 10 = 200\,\text{N}$.Mechanical advantage $\mathrm{MA} = \frac{W}{E} = \frac{200}{E}$, where $E$ is the effort.Efficiency formula: $\text{Efficiency}\% = \frac{\mathrm{MA}}{\mathrm{VR}} \times 100$.Given efficiency $= 100\%$, so:$100 = \frac{\frac{200}{E}}{5} \times 100$Cancel $100$ on both sides: $1 = \frac{200}{5E}$Thus, $5E = 200$$E = \frac{200}{5} = 40\,\text{N}$Answer:The effort required is $40\,\text{N}$, which is Option C.