Figure

Figure 24

$\mathbf{v}\;=\;\mathbf{r}^{\prime} (t)=\dfrac{dx}{dt}\mathbf{i} +\dfrac{dy}{dt}\mathbf{j}\\\;v = \left\Vert \mathbf{v}\right\Vert =\sqrt{\left( \dfrac{dx}{dt}\right) ^{2}+\left(\dfrac{dy}{dt}\right) ^{2}}.$