Question

Four identical balls, A, B, C and D are placed on a smooth horizontal plane such that B, C and D are in one line and are in contact and A is kept along the same line but a distance away. Now, A is set in motion with speed v along the line and it strikes the ball B. After this collision, which is elastic:

• A. Balls A, B, C will be at rest and D will move with speed v
• B. A will be at rest, where B, C and D will move together with speed $v/3$
• C. A will rebound with speed $v/2$ while B, C and D will move together with speed $v/2$
• D. A, B, C and D will move together with speed $v/4$

Hint:

For equal masses in elastic collision, velocities are exchanged.

Answer 1

The Correct Option is A

Step 1: Series of elastic collisions between equal masses.

Step 2: Velocities are exchanged. So A stops, B moves with v; then B hits C, B stops, C moves with v; then C hits D, C stops, D moves with v.