Question

A particle of mass m moving with a speed v hits elastically another stationary particle of mass 2 m on a smooth horizontal circular tube of radius r. The time in which the next collision will take place is equal to

• A. $\frac{2\pi r}{v}$
• B. $\frac{4\pi r}{v}$
• C. $\frac{3\pi r}{2v}$
• D. $\frac{\pi r}{v}$

Answer 1

The correct option is A $\frac{2\pi r}{v}$

Relative velocity of separation
= relative velocity of approach
= v (as e=1)
$\therefore$ Time of next collision $=\frac{2\pi r}{v}$