Two bodies have intial velocities directed towards each other. They collide at a position below the position where they would have collided in the absence of gravity. Gravity causes them to meet at a position gt2
/2 below where they would have met in the absence of gravity. Here t is the time they would have taken to meet in the absence of gravity and this t is d/(vRi
), where d is the intial distance between the positions of the bodies and vRi
are intial velocities of the red and blue bodies.
The red (vRi
t) and blue vectors (vBi
t ) along the line joining the initial positions represent the displacements of the bodies and the white vectors are equal to gt2
Observe the case when magnitudes of velocities of the two bodies are equal. The bodies would have met at the midpoint of the line joining them in the absence of gravity and they meet below that point as gravity accelerates them downward.