A particle is thrown above, then correct $v-t$ graph will be

In $1.0 \sec$ a particle goes from point $A$ to point $B$ moving in a semicircle of radius $1.0 \mathrm{m}.$ The magnitude of average velocity is

$50 \mathrm{m}$ long trains are crossing each other in opposite direction with velocity of $10 \mathrm{m} {\mathrm{s}}^{-1}$ and $15 \mathrm{m} {\mathrm{s}}^{-1}$ respectively. Then time-taken by trains to cross each other will be