Question

The force required to row a boat at constant velocity is proportional to the speed. If a speed of $4km{h}^{-1}$ requires $7.5\text{kW},$ how much power does a speed of $12km{h}^{-1}$ require?

Answer 1

$P=F.v$
where $P$ is power, $F$ is Force applied and $v$ is velocity.
$F$ is constant.
$P_1=7.5kW,P_2=?$
$v_1=4km{h}^{-1}$; $v_2=12km{h}^{-1}$
$P_2=\frac{P_1{v}_2}{v_1}$
$P_2=7.5\times 3=22.5kW$