Answer
The escape speed from this planet would be $22.4~km/s$
Work Step by Step
If the radius was twice the size of Earth's radius then the planet would have 8 times the volume. Since the density is the same, the planet's mass would be $8~M_E$.
We can find the escape speed from this planet:
$v_e = \sqrt{\frac{2~G~(8M_E)}{2R_E}}$
$v_e = 2~\sqrt{\frac{2~G~M_E}{R_E}}$
$v_e = (2)~(11.2~km/s)$
$v_e = 22.4~km/s$
The escape speed from this planet would be $22.4~km/s$.
