Question

A block and tackle system has $\mathrm{VR}=5$. Rahul exerts a pull of $150\mathrm{kgf}$. What is the maximum load he can raise with this pulley system if its efficiency $=75\%$?

• A. $500.2$
• B. $562.5$
• C. $661.5$
• D. $332.4$

Answer 1

The correct option is B

$562.5$

Step 1: Given data.

The velocity ratio $\left(\mathrm{VR}\right)=5$.

Effort applied is $150\mathrm{kgf}$.

Efficiency $\left(\eta \right)=75\%$

Step 2: Find the mechanical advantage

As we know,

$\begin{array}{rcl}\eta & =& \frac{\mathrm{Mechanical}\mathrm{advantage}\left(\mathrm{MA}\right)}{\mathrm{Velocity}\mathrm{ratio}\left(\mathrm{VR}\right)}\\ \frac{75}{100}& =& \frac{MA}{5}\\ \frac{3}{4}& =& \frac{MA}{5}\\ \mathrm{MA}& =& \frac{5\times 3}{4}\\ MA& =& \frac{15}{4}\end{array}$

Step 3: Find the maximum load Rahul can raise with this pulley system.

$$\begin{gathered} MA=\frac{Load}{Effort} \\ Load=Effort\times MA \end{gathered}$$

Therefore, the maximum load that can be raised is

$$\begin{gathered} =\mathrm{effort}\mathrm{applied}\times \mathrm{MA}\left(\mathrm{kgf}\right) \\ =150\times \frac{15}{4} \\ =562.5\mathrm{kgf} \end{gathered}$$

Hence, the correct option is (B).