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:

Question

( A ) $\sqrt{2s (\frac{1}{f} + \frac{1}{r})}$
( B ) $2s (\frac{1}{f} + \frac{1}{r})$
( C ) $\sqrt{2s ({f} + {r})}$
( D ) $\frac{2s}{\frac{1}{f} + \frac{1}{r}}$