Q 11-05-189JEE MainJEE Main 2019 (9 Apr, Shift 2)Easy
A particle of mass $m$ is moving with speed $2v$ and collides with a mass $2m$ moving with speed $v$ in the same direction. After the collision, the first mass is stopped completely while the second one splits into two particles each of mass $m$, which move at an angle $45^\circ$ with respect to the original direction. The speed of each of the moving particles will be
Answer: (C) $2\sqrt2v$
Initial momentum along the original direction: $m(2v) + 2m(v) = 4mv$.
After the collision, the two pieces move symmetrically at $45^\circ$, so their perpendicular components cancel and
$$2mu\cos45^\circ = 4mv \Rightarrow u = \frac{2v}{\cos45^\circ} = 2\sqrt2v$$
Solution by Sreeraj P, M.Sc Physics