Two boys are standing at the ends A and B of a ground where AB = a. The boy at B starts. running in a direction perpendicular to AB with velocity v1. The boy at A starts running simultaneously with velocity v and catches the other boy in a time t, where t is -

Question

( A ) $\frac {a}{v+v_1}$
( B ) $\sqrt\frac{a^2}{\sqrt{v^2-v^2_1}}$
( C ) $\frac {a}{v-v_1}$
( D ) $\frac{a}{\sqrt{v^2+v^2_1}}$