Question

A block and tackle system of 5 pulleys is capable of raising load of 300N vertically upward when an effort of 75 N is applied to it downward. Calculate the efficiency of the system

Answer 1

Calculate the mechanical advantage: it equals load over effort:

$$MA=L/E=300/75=4.$$

Calculate the velocity ratio: it equals to the number of pulleys:

$$VR=N_\text{p}=5.$$

Calculate the efficiency:

$$\eta=\frac{MA}{VR}\cdot 100\% = \frac{4}{5}\cdot 100\% =80 \%.$$