Two small particles of equal masses start moving in opposite directions from a point
A in a horizontal circular orbit. Their tangential velocities are v and 2v respectively,
as shown in the figure. Between collisions, the particles move with constant speeds.
After making how many elastic collisions, other than that at A, these two particles
will again reach the point A?
(A) 4 (B) 3
(C) 2 (D) 1

• Instantaneously before 1st collision, Particle X( wid initial speed v) has travelled an angular displacement of 120 deg and Particle Y( the other) has travelled an angular displacement of -240 deg. When they meet, X's velocity becomes 2v in d dirn opp to its initial motion and Y's velocity becomes v in d dirn opp 2 its initial motion.(due to perfectly elastic collision)
  They collide again when X makes -120deg with A (by a similar method as worked out above) and we see that they collide again @ 0deg. Thus, after 2 collisions will they be again @ A together
• 10 years agoHelpfull: Yes(0) No(0)