A block and tackle system has 5 pulleys. If an effort of 1250 N is needed in the downward direction to raise a load of 5000 N calculate(a) M.A. (b) V.R.(c)efficiency of the system. Also find the magnitude of extra force needed to overcome the friction. In this question it is said that the extra force needed to overcome the friction. Now according to the answer it is 3750 Newton. If that is true then how will the efficiency amount to 100% because considering the extra force and the actual force the total effort would be 5000 Newton then the mechanical advantage would be 1 and the efficiency would amount to 20% only. Then how will the friction be overcomed?

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Solution

Yes that is the correct answer
no. Of pulleys = v× r = 5
L = 5000
E. = 1250
so MA = L/E = 5000/1250
= 4
Efficiency =. MA /VR
=( 4/5) × 100
= 80%

Hence 20% percentage is used to overcome friction.

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