The height at which the acceleration due to gravity becomes $\frac { \mathrm { g } } { 9 }$ (where $\mathrm { g } =$ the acceleration due to gravity on the surface of the earth) in terms of $R$, the radius of the earth is\\
(1) $2 R$\\
(2) $\frac { R } { \sqrt { 2 } }$\\
(3) $\frac { R } { 2 }$\\
(4) $\sqrt { 2 } \mathrm { R }$