Time period of spring \(=2 \pi \sqrt{\frac{k}{m}}\)

Time period of pendulum \(=2 \pi \sqrt{\frac{l}{g}}\)

Time period of spring will not be affected by gravitational acceleration.

Let mass of earth be \(m\)

Mass of new planet \(=\rho \times \frac{4}{3} \pi(2 R)^3=8 m\)

\(g_2=\frac{G M_2}{\left(R_2\right)^2}=\frac{G \times 8 M}{(2 R)^2}=2 g\)

\(T_2=2 \pi \sqrt{\frac{I}{2 g}}\)

\(T_2=\frac{T}{\sqrt{2}}\)

Hence \(P\) will move faster.