A unit of power often used for electric motors is the horsepower (hp), which equals 746 W. A small electric car is equipped with a 40-hp electric motor. How much energy does the motor deliver in one hour, assuming the motor is operating at maximum power for the whole time?
1 Horse power \((\mathrm{hp})=746 \mathrm{~W}\)
The power is
$$ \begin{aligned} &p=40 \mathrm{hp} \\ &p=40 \times 746 \mathrm{~W} \\ &p=29840 \mathrm{~W} \end{aligned} $$
Energy delivered by the motor in one hour is
$$ \begin{aligned} &w=p t \\ &w=29840 \times 1(\mathrm{~h}) \times 60(\mathrm{~min} / \mathrm{h}) \times 60(\mathrm{~s} / \mathrm{min}) \\ &w=107424000 \\ &\therefore w=107.424 \mathrm{MJ} \end{aligned} $$