Question

A pulley system has $\mathrm{MA}=4$. If a load of $10\mathrm{kgf}$ is pulley by a distance of $2\mathrm{m}$ in $10\mathrm{s}$, calculate the power developed by the effort.

• A. $15\mathrm{w}$
• B. $20\mathrm{w}$
• C. $25\mathrm{w}$
• D. $4.9\mathrm{w}$

Answer 1

The correct option is C

$25\mathrm{w}$

Step 1: Given data,

Load $\left(\mathrm{L}\right)$ $=10\mathrm{kgf}$

Distance $\left(\mathrm{d}\right)=2\mathrm{m}$

Time $\left(\mathrm{t}\right)=10\mathrm{s}$

Acceleration due to gravity $\mathrm{g}=10\mathrm{m}/{\mathrm{s}}^2$

Step 2: Find the power output,

The load in terms Newton is,

$$\begin{gathered} L=10\times g \\ L=10\times 10 \\ L=100N \end{gathered}$$

$\begin{array}{rcl}\mathrm{power}\mathrm{input}& =& \frac{\mathrm{L}\times \mathrm{d}}{\mathrm{t}}\\ & =& \frac{100\times 2}{10\mathrm{s}}\\ & =& 20\mathrm{watt}\end{array}$

Step 3: Find the power input,

Power input (or power developed by the effort)$=\frac{\mathrm{power}\mathrm{output}}{\mathrm{efficiency}}$

$$\begin{gathered} =\frac{20\mathrm{w}}{0.8} \\ =25\text{w} \end{gathered}$$

Hence, the correct option is (C).