Question

Six identical balls are lined up along a straight frictionless groove. Two similar balls moving with speed v along the groove collide elastically with this row on extreme left side end. Then

• A. One ball from the right end will move on with speed 2v, all the other remains at rest.
• B. Two balls from the extreme right will move on with speed v each and the remaining balls will be at rest.
• C. All the balls will start moving to right with speed v/8 each.
• D. All the six balls originally at rest will move on with speed v/6 each and the two incident balls will come to rest.

Answer 1

The correct option is B Two balls from the extreme right will move on with speed v each and the remaining balls will be at rest.

The two particles having equal mass exchange their respective velocities after a head-on perfectly elastic collision.

Thus when the two similar balls moving with speed $v$ collide elastically with the row on extreme left end, then the two balls from the extreme right end move with the speed $v$ each while the other remaining balls remain at rest.