Question

lucy needs to lift a crate to a shelf 20 m high. she does 12,000 j of work on a machine to help her. the machine exerts a force of 500 n to lift the crate. what is the efficiency of the machine? 4.2% 24% 58% 83%

Explanation:

Step1: Calculate useful work output

Use the formula $W = Fd$, where $F = 500\ N$ and $d=20\ m$. So $W_{useful}=F\times d = 500\times20=10000\ J$.

Step2: Calculate efficiency

The formula for efficiency $\eta$ is $\eta=\frac{W_{useful}}{W_{input}}\times100\%$. Given $W_{input} = 12000\ J$ and $W_{useful}=10000\ J$. Then $\eta=\frac{10000}{12000}\times 100\%\approx 83.33\% \approx 83\%$.

Answer:

83%