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Question
(a) Fig represents an incomplete diagram of a simple string pulley system. Copy this diagram on a new page and complete it and mark where the effort must be applied to lift the load.
(b) What is the velocity ratio of this system?
(c) If the pulley system is 80% efficient and the load is 720 N, then
(i) What effort must be applied to lift the load?
(ii) What work must be done must be done in lifting the load through a distance of 2 m using this machine?
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Solution
a) Corrert wínding ofrope around pulleys, load and effortis as shown
b) Since there are four strings in the block and tackle system, therefore, the velocíty ratio ofthe systemís V.R = n = 4
c)
(i) Given load L = 720 N
Let effort = E
Efficiency = `"M.A"/"V.R"`
or, 80% = `"L/E"/4`
or, `80/100 xx 4 = 720/E`
or, E = `(720 xx 100)/(80 xx 4)` = 225 N
(ii) Given, Load L = 720 N
Displacement - of - load, dL = 2m
Efficiency = `"work - output"/"work - input"`
or work - input = `"work - output"/"efficiency" = ("Load" xx "d"_"L")/"n"`
or, Work - input = `(720 xx 2)/0.8` = 1800 J
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