Q.
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
Explanation
(c) A s first collision one particle having speed 2v will rotate
$240{^\circ}\left( or\frac{4\pi}{3} \right)$while other particle having speed $v\ $will rotate
$120{^\circ}\left( or\frac{2\pi}{3}\ \right).$ At first collision they will exchange their velocities. Now as shown in figure, after two collisions they will again reach at point A.
[image:6_image87.emf]
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.