Question

Three balls A, B and C of same mass m are placed on a frictionless horizontal plane in a straight line as shown. Ball A is moved with velocity u towards the middle ball B.

If all the collisions are elastic then, find the final velocities of all the balls A, B, and C respectively:

• A. u,u, u
• B. u, 0, u
• C. 0, u, u
• D. 0, 0, u

Answer 1

The correct option is D 0, 0, u

Answer is D.
After a while B collides elastically with C and comes to rest but C starts moving with velocity $u$ .

Final velocities.

$V_A=0;$

$B_B=0$ and $V_C=u$

A collides elastically with B and comes to rest but B starts moving with velocity $u$, B further collide with C and it comes to rest imparting the velocity $u$ to C.

Please refer diagram.
Therefore, the final velocities of A, B, and C are 0, 0 and u respectively.