Elastic collisions

2015 AIPMT-II 1 question

1. 1 Work, Energy and Power
   On a frictionless surface, a block of mass M moving at speed v collides elastically with another block of same mass M which is initially at rest. After collision the first block moves at an angle $\theta$ to its initial direction and has a speed $\frac{v}{3}$. The second block's speed after the collision is:
   A $\frac{3}{\sqrt2}v$ B $\frac{2\sqrt2}{3}v$ C $\frac{3}{4}v$ D $\frac{\sqrt3}{2}v$
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