On a frictionless surfaces, 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:

1. A
   $\frac{\sqrt{3}}{2}v$
2. B
   $\frac{2\sqrt{2}}{3}v$
3. C
   $\frac{3}{4}v$
4. D
   $\frac{3}{\sqrt{2}}v$