A system with one fixed and one moveable pulley operates with 90% efficiency. The moveable pulley has a weight of 5 N. Using this pulley system, what is the minimum input force needed to lift a piano weighing 1,595 N?

Answer

800 N

Explanation

Efficiency = (mechanical advantage) / (velocity ratio) * 100%

Mechanical advantage (M. A) = Load/Effort

= (1,595+5) / Effort

= 1,600/Effort

Velocity ratio = 2

90/100 = M. A/2

M. A = 0.9 * 2

= 1.8

M. A = 1,600/Effort

2 = 1,600/Effort

Effort = 1600/2

= 800 N

Answer: C. 889 N

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