Draw a diagram of combination of three movable pulleys and one fixed pulley to lift up a load. In the diagram, show the directions of load, effort and tensiom in each strand. Find : (i) the mechanical advantage , (ii) the velocity ratio, and (iii) the efficiency of the combination, in the ideal situation.

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Solution

(i) Mechanical advantage = MA = L/E = 2³

(ii)
As one end of each string passing over a movable pulley is fixed, so the free end of string moves twice the distance moved by the movable pulley.
If load L moves up by a distance x, d_L = x, effort moves by a distance 2³x, d_E = 2³x
$V e l o c i t y space r a t i o equals fraction numerator D i s tan c e space m o v e d space b y space t h e space e f f o r t space d subscript E over denominator D i s tan c e space m o v e d space b y space t h e space l o a d space d subscript L end fraction equals fraction numerator 2 cubed x over denominator x end fraction equals 2 cubed$

(iii)
$E f f i c i e n c y b equals fraction numerator M A over denominator V R end fraction equals 2 cubed over 2 cubed equals 1 space space o r space 100 percent sign$

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