Question

Five identical elastic balls are so suspended with strings of equal length in a row that the distances between adjacent balls are very small. If the extreme right ball is moved aside and released, then:

• A. one extreme left hand ball will bounce off
• B. two extreme left hand balls will bounce off
• C. three extreme left hand balls will bounce off
• D. all the left hand four balls will bounce off

Answer 1

The correct option is A one extreme left hand ball will bounce off

As motion of all balls are elastic and of same mass, when one hits another, their momenta is exchanged.

1 -> 2, 1 comes to rest and 2 moves.

2 -> 3, 2 comes to rest and 3 moves.

3 -> 4, 3 comes to rest and 4 moves.

4 -> 5, 4 comes to rest and 5 moves.

Now, 5 has no obstacle .Thus will move.