Question

Suppose a planet has twice the mass of the earth and twice the earth's radius. What is the acceleration of an object in free fall on this planet?
2.5 m/s2

4.9 m/s2

9.8 m/s2

4.9 × 106 m/s2

...?

Answer 1

We use the equation:

g = G m / r2 
where
G=constant universal gravitational = 6.67 x 10^-11 n m^2/kg^2 
m=planet mass=5.9736 x 10^24 kg (twice=11.9472) 
r radium planet=6.372 km (twice=12.744) 

g= 6.67 x 10^-11 n m^2/kg^2 x 11.9472 10^24 kg/(12.744.000m)^2 
g=4.90 m/s^2 (1/2 of Earth gravity)  <------- second option