Figure shows a block and tackle system of pulleys used to lift a load.

(a) How many strands of tackle are supporting the load?

(b) Draw arrows to represent tension T in each strand.

(c) What is the mechanical advantage of the system?

(d) When load is pulled up by a distance 1 m, how far does the effort end move?

(e) How much effort is needed to lift a load of 100 N?

(f) What will be its V.R. if the weight of the movable block is doubled?

(a) There are 4 strands of tackle supporting the load.

(b) Tension T in each strand is as shown in the diagram below:

(c) As we know,

$M.A. = \dfrac{\text {Load}}{\text {Effort}} \\[0.5em]$

Load = 4T

Effort = T

Substituting the values in the formula for M.A. we get,

$M.A. = \dfrac{4T}{T} \\[0.5em]$

Hence, M.A. = 4

(d) In a system of 4 pulleys, if the load moves up through a distance 1m, each segment of the string is loosened by a length 1m so the effort end moves through a distance 4 times 1m. Hence, we get 4m as the distance moved by the effort arm.

(e) As we know,

$M.A. = \dfrac{\text {Load}}{\text {Effort}} \\[0.5em]$

M.A = 4

Load = 100 N

Substituting the values in the formula for M.A. we get,

$4 = \dfrac{100}{\text{Effort}} \\[0.5em] \text{Effort} = \dfrac{100}{4} \\[0.5em] \Rightarrow \text{Effort} = 25N \\[0.5em]$

(f) V.R = n (number of pulleys) = 4