Two particles A and B move with constant velocities and . At the initial moment their position vectors and respectively. The condition for particles and for their collision is: (1) (2) (3) (4)

The correct Solution is (2)
For two particles to collide, the direction of the relative velocity of one with respect to other should be directed towards the relative position of the other particle
i.e. direction of relative position of 1 w.r.t. 2 .
direction of velocity of 2 w.r.t. 1
So for collision of ]