The object at rest suddenly explodes into three parts with the mass ratio 2:1:1.The parts of equal masses move at right angles to each other with equal speed ‘v ’.the speed of the third part after explosion will be

• A

  v

• B

  $\sqrt{2}\mathrm{v}$

• C

  $\frac{\mathrm{v}}{2}$

• D

  $\frac{\mathrm{v}}{\sqrt{2}}$