Question

Raghav applies a force of 6kgf to draw 4.8kg bucket of water from a well using a single fixed pulley. Assuming that all of the extra force a applied is to overcome frictional forces, calculate the force of friction, mechanical advantage and efficiency.

Answer 1

$$\begin{gathered} \mathrm{Given}\mathrm{that} \\ \mathrm{E}=6\mathrm{kgf}=6\times 10\mathrm{N}=60\mathrm{N} \\ \mathrm{L}=4.8\mathrm{kgf}=4.8\times 10\mathrm{N}=48\mathrm{N} \\ \mathrm{E}=\mathrm{T}=\mathrm{L}+\mathrm{friction}\mathrm{force} \\ \mathrm{So},\mathrm{friction}\mathrm{force},\mathrm{f}=\mathrm{E}-\mathrm{L}=60-48=12\mathrm{N} \\ \mathrm{Mechanical}\mathrm{advantage}=\mathrm{L}/\mathrm{E}=48/60 \\ =0.80\mathrm{N} \\ \mathrm{Now},\mathrm{efficiency}\mathrm{\eta }=\mathrm{Mechanical}\mathrm{advantage}\left(\mathrm{MA}\right)/\mathrm{Velocity}\mathrm{ratio}\left(\mathrm{VR}\right) \\ \mathrm{For}\mathrm{a}\mathrm{single}\mathrm{fixed}\mathrm{pulley}, \\ \mathrm{VR}=1 \\ \mathrm{So}, \\ \mathrm{\eta }=\mathrm{MA}/1=0.80/1=0.80 \\ \mathrm{Or}80\% \end{gathered}$$