question_answer

Two small particles of equal masses start moving in opposite directions from 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

Correct Answer: C

Solution :

[c] : At first collision, particle having speed 2v will rotate by \[240{}^\circ \]\[\left( or\frac{4\pi }{3} \right)\]while other particle having speed v will rotate by \[120{}^\circ \] \[\left( or\frac{2\pi }{3} \right)\]. At first collision, they will exchange their velocities. Now as shown in figure, after two collisions they will again reach at point A.