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Question
The diagram below shows a pulley arrangement.
(i) In the diagram, mark the direction of the forces due to tension, acting on the pulley P.
(ii) What is the purpose of the pulley Q?
(iii) If the tension is T newton, deduce the relation between T and E.
(iv) Calculate the velocity ratio of the arrangement.
(v) Assuming that the efficiency of the system is 100%, what is the mechanical advantage?
(vi) Calculate the value of E
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Solution
(ii) The purpose of the pulley Q is to change the direction of application of effort to a convenient direction.
(iii) In the diagram, T = E
(iv) If the free end of the string moves, through the distance x, the load will rise by a distance x/2.
Threfore, V.R = distance moved y the effort arm / distance moved by the load = `"x"/("x"//2) = 2`
(v) In equilibrium,L = 2T and E = T
efficiency = M.A / V. R
or, 1 = `("M ""A")/2`
⇒ M.A = 2
(vi) M.A = `"L"/"E"`
⇒ E = `"L"/("M"."A") = 100/2` = 50 N
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