A body travels a distance $s$ in $t$ seconds. It starts from rest and ends at rest. In the first part of the journey, it moves with constant acceleration $f$ and in the second part with constant retardation $r$. The value of $t$ is given by\\
(1) $\sqrt{2s\left(\frac{1}{f} + \frac{1}{r}\right)}$\\
(2) $2s\left(\frac{1}{f} + \frac{1}{r}\right)$\\
(3) $\frac{2s}{\frac{1}{f} + \frac{1}{r}}$\\
(4) $\sqrt{2s(f + r)}$