1. The problem statement, all variables and given/known data Here is the text of the question: "A satellite circles planet Roton every 2.8 h in an orbit having a radius of 1.2 X 10^7 m. If the radius of Roton is 5.0 X 10^6 m, what is the magnitude of the free-fall acceleration on the surface of Roton?" 2. Relevant equations v=d/t M= [(Ve)^2*R]/(2G) a=GM/r^2 3. The attempt at a solution This is presented as multiple choice, and I've been able to find the answer as 27 m/s^2 but I haven't been able to figure it out on my own. What I tried to do is find the mass of Roton using the orbit speed. I took the distance traveled by the satellite, 2*pi*1.2e7, and diving it by the time of one complete orbit, 2.8 hr or 10080 s. I calculated this velocity as 7479.98 m/s. To find mass, I used the second formula I listed, and used the radius of Roton as R. I'm not sure if this is correct. I used this mass in the third formula, using the sum of Roton's radius plus the orbit radius. I think this may also be incorrect. I got an answer that was significantly different than the multiple choice answers provided. Can someone steer me in the right direction?