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**Mechanical advantage, Efficiency and WO WI**

Simple machines

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**Work output, work input W = Fd**

Using a block and tackle, you supply an effort force of 250N and move the rope 3m. The load being lifted is 750N and moves a distance of 1m. What is the work input and work output? W = Fd; 250N x 3m = 750J W = Fd; 750N x 1m = 750J

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**Efficiency of a machine**

Efficiency = Work Output ÷ work input x 100 Express as a percentage (%) A force of 1200N is needed to move a box up a ramp. The ramp is 4m long. The ramp raises the 3200N resistance (load) to a height of 1 m. What is the work output, the work input and the efficiency of the ramp? Work input: W = Fd; 1200N x 4m = 4800J Work output: W = Fd; 3200N x 1m = 3200J Efficiency: 3200J ÷ 4800J x 100 = .67 x 100 = 67%

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**Mechanical Advantage for a lever or inclined plane**

MA = Resistance force ÷ Effort force MA = R ÷ E MA = Effort distance ÷ Resistance distance (length of ramp ÷ height of ramp) MA = ED ÷ RD MA = Effort arm ÷ Resistance arm MA = EA ÷ RA

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**Mechanical advantage for a pulley**

Count the number of strands of rope that support the load or resistance force 1 fixed pulley – 1 1 moveable pulley – 2 2 fixed and one moveable pulley – 3 2 fixed and 2 moveable pulleys – 4

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Work, Machines, and Energy

Work, Machines, and Energy

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