A round disc of moment of inertia I₂, about its axis perpendicular to its plane and passing through its centre is placed over another disc of moment of inertia I₁, rotating with an angular velocity $\mathrm{\omega }$about the same axis. The final angular velocity of the combination of discs is

• A

  $\frac{{\mathrm{I}}_2\mathrm{\omega }}{{\mathrm{I}}_1+{\mathrm{I}}_2}$

• B

  $\mathrm{\omega }$

• C

  $\frac{{\mathrm{I}}_1\mathrm{\omega }}{{\mathrm{I}}_1+{\mathrm{I}}_2}$

• D

  $\frac{\left({\mathrm{I}}_1+{\mathrm{I}}_2\right)\mathrm{\omega }}{{\mathrm{I}}_1}$