Answer :
We need at least one pulley to lift the load of 200 lb with an overhead system using pulleys that have an efficiency of 0.9, given that we can provide a maximum input force of 103 lb.
Assuming that the weight of the pulleys and the rope is negligible, we can use the formula,
Load = (Input Force / Efficiencies) ^ Number of Pulleys
where Load is the weight of the load we want to lift, Input Force is the force we apply to the system, Efficiency is the efficiency of each pulley, and Number of Pulleys is the number of pulleys we need.
Plugging in the given values,
200 lb = (103 lb / 0.9) ^ Number of Pulleys
Simplifying the equation,
Number of Pulleys = log (base 2) (200 / (103/0.9))
Number of Pulleys = log (base 2) (200 x 0.9 / 103)
Number of Pulleys = log (base 2) 1.983495
Number of Pulleys = 1
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