a recently discovered exoplanet ( a planet orbiting another star) has a mass that is twice of the earth, and a radius that is three times that of the earth. what is the value of g at the planet's surface? ignore the planet's rotation.

Question

anonymous · Answer

You know that the force of gravity is proportional to the mass of the object, and inversely proportional to the square of the distance from the center of mass of the object. 

$$F = \frac{ G Mm }{ r^2 }$$

$$g$$ is the simple form of $$\frac{ GM }{ r^2 }$$ on Earth. Since the mass of this planet is double the mass of the Earth, the force of gravity is doubled. But since you are 3 times as far away from the center of the planet at the surface than you are on the Earth's surface, the force of gravity goes down by a factor of 9.

anonymous · Answer

thank you so much

anonymous · Answer

so i plug the numbers in? or its just the formula?