Two particles P and Q each of mass 3m lie at rest on the X-axis at point (-a,0) and (+a,0) respectively. A third particle R of mass 2m intially at the origin moves towards the particle Q. IF all the collisions of the system of 3 particles are elastic and head on, the total number of collisions in the system is

Options

A. 2
B. 3
C. 4
D. 5

Explanation

According to question, three particles are situated as shown below,

`because` All the collision of the system of 3 particles are elastic and head on.
So, collisions of R and Q,

Hence R and Q will never collide after 1st collision.
`therefore` Total number of collision is 2.