What would the gravitational field strength be on a planet with twice Earth's mass and twice its radius?

78.4 N/kg
39.2 N/kg
19.6 N/kg
9.8 N/kg
4.9 N/kg

a = G M / R^2      acceleration due to gravity

aE /aP = (ME / RE^2) / (MP / RP^2) = (ME / MP) * (RP^2 / RE^2)

Since MP = 2 ME   and RP = 2 RE

aE / aP = 1/2 * 2^2 = 2

So the gravitational field strength of the planet is 1/2 that of the earth or 4.9 N/kg

dang that balls went far