1 Conversion: Vacuum Cleaner
Your $18~{\rm V}$ vacuum cleaner is equipped with a $4.0~{\rm Ah}$ battery, it runs $15~{\rm minutes}$.
How much electrical power is consumed by the motor during this time on average?
\begin{align*}
W &= 18~{\rm V} \cdot 4.0~{\rm Ah} = 72~{\rm Wh} \\ \\
t &= 15~{\rm min} = 0.25~{\rm h} \\ \\
P &= {{W } \over {t }} \\
&= {{72~\rm Wh} \over {0.25~\rm h }} = 288~{\rm W}
\end{align*}
\begin{align*}
288~{\rm W}
\end{align*}