Centre of Mass 3 Question 14
17. 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 $2 v$ 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 $A$ ?
(2009)
(a) 4
(b) 3
(c) 2
(d) 1
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Answer:
Correct Answer: 17. (c)
Solution:
- At first collision one particle having speed $2 v$ will rotate $240^{\circ}$ or $\frac{4 \pi}{3}$ while other particle having speed $v$ will rotate $120^{\circ}$ or $\frac{2 \pi}{3}$. At first collision, they will exchange their velocities. Now, as shown in figure, after two collisions they will again reach at point $A$.
