Question

Figure shows a block and tackle system of pulleys used to lift a load. How much effort is needed to lift a load of $100N$?

Answer 1

Given:
The block and tackle system consists of 4
pulleys, i.e. $n=4$
In a n-pulley block and tackle system, if the effort is applied in the downward direction then the tension in the n segments of the string supports the load.
$L=nT\text{and}E=T$
Hence, Mechanical advantage
$M.A.=\frac{loadL}{effortE}=\frac{nT}{T}=n=4$
Thus, the mechanical advantage is equal to the number of pulleys in both the blocks.
Given:
Load $L=100N$
$M.A.=4$
We know
$M.A.=\frac{LoadL}{EffortE}$
Thus, the effort required,
$E=\frac{L}{M.A.}=\frac{100N}{4}=25N$