What is the particle's velocity ds/dt?

Explanation

1. 01

   $\frac{d}{dt}\sqrt{u} = \frac{u'}{2\sqrt{u}}$ with $u = t^{2} + 16$.

2. 02

   $\frac{2t}{2\sqrt{t^{2} + 16}} = \frac{t}{\sqrt{t^{2} + 16}}$.