Explanation

(c) Let initially particle $x$ is moving in anticlockwise direction and $y$ in clockwise direction
As the ratio of velocities of $x$ and $y$ particles are $\frac{v_{x}}{v_{y}} = \frac{1}{2}$, therefore ratio of their distance covered will be in the ratio of $2\ :1$. It means they collide at point B
[image:6_image74.emf]
After first collision at B, velocities of particles get interchanged, $i.e$., $x$ will move with $2v$ and particle $y$ with $v$
Second collision will take place at point C. Again at this point velocities get interchanged and third collision take place at point A
So, after two collision these two particles will again reach the point A