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  $\frac{\mathrm{v}}{2}$

• B

  Both P and Q move forward with speed $\frac{\mathrm{v}}{\sqrt{2}}$

• C

  P comes to rest and Q moves forward with speed v

• D

  P and Q move in opposite directions with speed  $\frac{\mathrm{v}}{\sqrt{2}}$