Planet X has three....

Question

Planet X has three Earth's mass and twice times Earth's radius. The magnitude of the gravitational field near Planet X's surface is most nearly... 

a. 2 m/s^2 

b. 7 m/s^2 

c. 10m/s^2 

d. 20 m/s^2 

(The answer should be b, 7m/s^2) 

Answer 1

What you need to do is calculate the acceleration of gravity on the surface of Planet X.

 

M_e = mass of earth

R_e = radius of earth

 

g_x = GM_x/R_x² = G(3M_e)/(2R_e)² = 0.75(GM_e/R_e²) = 0.75g = 0.75(9.8 m/s²) = 7.35 m/s²

 

Answer (b) is close.