2. $\sqrt{t} = t^{1/2}$
Then you can use the power law as normal to find $\dfrac{dx}{dt}$
3. If $f(x) = \sqrt{g(x)}$, then $f'(x) = \frac{g'(x)}{2\sqrt{g(x)}}$. I find that very handy for both integration and differentiation.