Question

Two particles $P$ and $Q$ each of mass $3m$ lie at rest on the X-axis at points $(-a,0)$ and $(+a,0)$, respectively. A third particle $R$ of mass $2m$ initially 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

• A. 2
• B. 3
• C. 4
• D. 5

Answer 1

Answer: (A)

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, collision of $R$ and $Q$

Hence, $R$ and $Q$ will never collide after 1st collision.
$\therefore$ Total numbers of collision is $2$