Two particles start simultaneously from the same point and move along two straight lines, one with uniform velocity $\overrightarrow{u}$ and the other from rest with uniform acceleration $\overrightarrow{f}$. Let $\alpha$ be the angle between their directions of motion. The relative velocity of the second particle w.r.t. the first is least after a time :

Question

( A ) $u \sin \alpha$
( B ) $\frac{u \cos \alpha}{f}$
( C ) $\frac{u \sin \alpha}{f}$
( D ) $\frac{f \cos \alpha}{u}$