Consider elastic collision of a particle of mass m moving with a velocity u with another particle of the same mass at rest. After the collision the projectile and the struck particle move in directions making angles $\theta_{1}$ and $\theta_{2}$ respectively with the initial direction of motion. The sum of the angles $\theta_{1}+\theta_{2},$ is :

• A

  $45^{\circ}$
• Correct answer
  B

  $90^{\circ}$
• C

  $135^{\circ}$
• D

  $180^{\circ}$

Hence, the correct answer is option: 'B'.