The escape velocity from the earth is about $11 \mathrm{kms}^{-1}$. The escape velocity from a planet having twice the radius and the same mean density as the earth is $=\ldots \ldots \ldots \ldots \mathrm{kms}^{-1}$.
(A) 22
(B) 11
(C) $5.5$
(D) $15.5$