What is Power?

Example 9.16 (Kettle versus human)

A $2200\,\mathrm{W}$ kettle running $150\,\mathrm{s}$ uses $E = 2200 \times 150 = 3.3 \times 10^{5}\,\mathrm{J}$. A human runs on about $10\,\mathrm{MJ}$ of food per day, an average $1.0 \times 10^{7}/86\,400 \approx 116\,\mathrm{W}$: you idle like a bright old light bulb.

Example 17.15 (Crane)

A crane hoists a $600\,\mathrm{kg}$ pallet at a steady $0.90\,\mathrm{m}/\mathrm{s}$: the cable’s force equals the weight, $mg = 5.89 \times 10^{3}\,\mathrm{N}$, so $P = Fv = 5890 \times 0.90 \approx 5.3\,\mathrm{kW} \approx 7.2\,\mathrm{hp}$ — a seven-horse team in a steel box.