Example from Physics, 9.3 Simple Machines

Efficiency of a Lever

The input force of 11 N acting on the effort arm of a lever moves 0.4 m, which lifts a 40 N weight resting on the resistance arm a distance of 0.1 m. What is the efficiency of the machine?

Work it out on paper first. Then open the solution one step at a time, and stop as soon as you can finish on your own.

Strategy
State the equation for efficiency of a simple machine, $% efficiency = \frac{W_{o}}{W_{i}} \times 100,$ and calculate W_o and W_i. Both work values are the product Fd.
Solution
$W_{i} = F_{i} d_{i}$ = (11)(0.4) = 4.4 J and $W_{o} = F_{o} d_{o}$ = (40)(0.1) = 4.0 J, then $% efficiency = \frac{W_{o}}{W_{i}} \times 100 = \frac{4.0}{4.4} \times 100 = 91 %$

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