A particle of mass m with an initial velocity $$u\hat{i}$$ collides perfectly elastically with a mass 3m at rest. It moves with a velocity $$v\hat{j}$$ after collision, then, v is given by:

A

$$v = \sqrt{\frac{2}{3}}u$$

B

$$v = \frac{u}{\sqrt{3}}$$

C

$$v = \frac{u}{\sqrt{2}}$$

D

$$v = \frac{1}{\sqrt{6}}u$$