Q. Three identical balls $A,B\ $ and $C$ are lying on a horizontal frictionless table as shown in figure. If ball $A$ is imparted a velocity $v$ towards $B$ and $C$ and the collisions are perfectly elastic, then finally
A) Ball $A$ comes to rest and balls $B$ and $C$ roll out with sped $v/2$ each
B) Ball $A$ and $B$ are a rest and ball $C$ roll out with speed $v$
C) All the three balls roll out with speed $v/3$ each
D) All the three balls come to rest
Explanation
(b) When two identical balls collide head on elastically, they exchange their velocities. Hence when $A$ collides with $B$, $A$ transfers its whole velocity to $B$. When $B$ collides with $C$, $B$ transfers its whole velocity to $C$. Hence finally $A$ and $B$ will be at rest and only $C$ will be moving forward with speed $v$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.