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Question
In following figure, shows a block and tackle system of pulleys used to lift a load.
- How many strands of tackle are supporting the load?
- Draw arrows to represent tension T in each strand.
- What is the mechanical advantage of the system?
- When load is pulled up by a distance 1 m, how far does the effort end move?
- How much effort is needed to lift a load of 100 N?
- What will be it's V.R. if the weight of the movable block is doubled?
Solution
(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
dL = 1m = d
distance moved by effort = dE = 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
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