If a planet consists of a satellite whose mass and radius were both half that of the earth, the acceleration due to gravity at its surface would be

Given that

${\text{R}}_{\text{P}}=\frac{{\text{R}}_{\text{E}}}{\text{2}}$                                 

${\text{M}}_{\text{P}}=\frac{{\text{M}}_e}{\text{2}}$ 

Acceleration due to gravity is given by:
$g=\frac{GM}{R^2}$
Acceleration due to gravity of the planet can be given by                              

${\text{g}}^{\text{1}}=\frac{{\text{GM}}_{\text{P}}}{{\text{R}}_{\text{P}}^{\text{2}}}=\frac{{\text{GM}}_{\text{e}}\text{/2}}{{\left({\text{R}}_{\text{e}}\text{/2}\right)}^{\text{2}}}$

$\Rightarrow {\text{g}}^{\text{1}}=\frac{{\text{GM}}_{\text{e}}}{\text{2}}\times \frac{\text{4}}{{\text{R}}_{\text{e}}^{\text{2}}}$

${\text{g}}^{\text{1}}=\frac{{\text{2GM}}_{\text{e}}}{{\text{R}}_{\text{e}}^{\text{2}}}$

$\because \frac{{\text{GM}}_{\text{e}}}{{\text{R}}_{\text{e}}^{\text{2}}}\left(\text{g}=9.8{\text{m/s}}^{\text{2}}\right)$

${\text{g}}^1=19.6{\text{m/s}}^{\text{2}}$