An experiment is being conducted inside a vacuum chamber. A particle of mass M moving at a speed of V is made to collide elastically with a stationary particle of mass 3M within the chamber. After the collision, the lighter particle gets scattered at a 90° angle. Determine the angle at which the heavier particle recoils following the collision.

• A. $0^{o}$
• B. $35^{o}$
• C. $55^{o}$
• D. $90^{o}$

Answer: (B)