(a) For particle $P$, motion between $A$ and $C$ will be an accelerated one while between $C$ and $B$ a retarded one. But in any case horizontal component of it’s velocity will be greater than or equal to $v$ on the other hand in case of particle $Q$, it is always equal to $v$. Horizontal displacement of both the particles are equal, so $t_{P} < t_{Q}$