Question

A manchine with an efficiency 80% is used to raise a body of mass 75kg through a vertical height of 3m in 30s calculate the power input taking g=10ms-2

Answer 1

$$\rm The\: efficiency=\frac{Output\:power}{Input\:power}$$ $$\eta=\frac{mgh/t}{P}$$

So, the input power

$$P=\frac{mgh}{\eta t}=\frac{75\times 10\times 3}{0.8\times 30}=93.75\:\rm W$$

Answer: $93.75\:\rm W$