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Question
Draw a diagram of a single fixed pulley and obtain expressions for its:
(i) Mechanical advantage,
(ii) Velocity ratio, and
(iii) Efficiency, in the ideal case.
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Solution
The diagram of a single fixed pulley is shown alongside. If T is the tension in each strand of the string and in the ideal case string is massless and there is no friction in the pulley bearings, then in equilibrium, E = T and L = T
(i) Mechanical advantage = `"L"/"E"="T"/"T"=1`
(ii) If the effort E moves a distance d downwards, the load L moves the same distance d upwards.
So, velocity ratio = `"d"_"E"/"d"_"L"="d"/"d"=1`
(iii) Efficiency =`"M.A."/"V.R."=1/1` = 1 (or 100%).
RELATED QUESTIONS
A pulley system has three pulleys. A load of 120 N is overcome by applying an effort of 50N. Calculate the Mechanical Advantage and Efficiency of this system.
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(i) Copy the diagram and mark the direction of tension on each strand of the string.
(ii) What is the velocity ratio of the arrangement ?
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