Question

In following figure, shows a block and tackle system of pulleys used to lift a load.

1. How many strands of tackle are supporting the load?
2. Draw arrows to represent tension T in each strand.
3. What is the mechanical advantage of the system?
4. When load is pulled up by a distance 1 m, how far does the effort end move?
5. How much effort is needed to lift a load of 100 N?
6. What will be it's V.R. if the weight of the movable block is doubled?

Answer 1

(a) 4 stands marked 1, 2, 3, and 4 support the load L.

(b) The strands' tension in the T direction is shown.

(c) M.A. = L = 4T and E = T

M.A. = `L/E`

= `(4T)/T = 4`

(d) As load is pulled up by 1 m

d_L = 1m = d

distance moved by effort = d_E = nd

V.R. = `d_E/d_L`

= `(nd)/d`

= n = 4m

(e) E = ?

L = 100 N, M.A. = 4

M.A. = `L/E`

`4 = 100/E` 

∴ 4E = 100

E = `100 / 4`

E = 25 N

(f) Velocity Ratio of the system = No. of Pulleys = 4