Clearly the two particles are at the two ends of the diameter of a circular path. It is further clear that each particle will return to its initial position after describing one circle.
If t = required time then,
t = \(\frac{2\pi r}{v}=\frac{\pi d}{v}\)
Where,
v = speed of particles.
r = radius of the circular track
d = constant distance between particles
2r = diameter of the circular path
