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Asked by sayeedafatima250 | 09 Apr, 2021, 10:12: AM
Let n be number of pulleys , T be tension in the cord and f is total friction force in the system ,
then we have

L + f = n T = n E

where E is effort which is equal to Tension T

Hence , number of pulleys n =  ( L + f ) / E .............. (1)

Let us assume acceleration due to gravity g = 10 m/s2 .

friction force f = 300 N = 300 /10 = 30 kgf

Hence number of pulleys n is determined from eqn.(1)

n = ( 120 + 30 ) / 25  = 6

Mechanical advantage MA = ( L / E ) = [ ( n E ) - f ] / E = n - ( f / E ) = 6 - ( 30/25) = 4.8

Velocity ratio VR = number of pulleys = n

Efficiency =  ( MA ) / ( VR ) = 4.8 /6 = 0.8
Answered by Thiyagarajan K | 09 Apr, 2021, 04:22: PM

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