\(\Rightarrow \frac{{{g_{{\rm{earth}}}}}}{{{g_{{\rm{planet}}}}}} = \frac{{{M_e}}}{{{M_p}}} \times \frac{{R_\rho ^2}}{{R_e^2}} \)
\(\Rightarrow \frac{{{g_e}}}{{{g_p}}} = \frac{2}{1}\)
Also \(T \propto \frac{1}{{\sqrt g }} \)
\(\Rightarrow \frac{{{T_e}}}{{{T_p}}} = \sqrt {\frac{{{g_p}}}{{{g_e}}}}\)
\(\Rightarrow \frac{2}{{{T_p}}} = \sqrt {\frac{1}{2}} \)
\( \Rightarrow \) \({T_p} = 2\sqrt 2 \,\sec \).