A hollow sphere rolls down a 30° incline of length 6m without slipping. The speed of centre of mass at the bottom of plane is

• A

  6ms^-1

• B

  3ms^-1

• C

  $6\sqrt{2}{\mathrm{ms}}^{-1}$

• D

  $3\sqrt{2}{\mathrm{ms}}^{-1}$