A particle `P` moving with speed `v` undergoes a head - on elastic collision with another particle `Q` of identical mass but at rest. After the collision
A. Both `P` and `Q` move forward with speed `(v)/(2)`
B. Both `P` and `Q` move forward with speed `(v)/(sqrt(2))`
C. `P` comes to rest and `Q` moves forward with speed `v`
D. `P` and `Q` move in opposite directions with speed `(v)/(sqrt(2))`