1. The problem statement, all variables and given/known data The trajectory of a rock thrown from a height with an initial speed of 16.9 m/s is shown in the figure below. Evaluate the magnitude of the gravitational field at the surface of the planet. The planet has no atmosphere. The graph is as follow: http://i995.photobucket.com/albums/af79/huybinhs/plot-1.png 2. Relevant equations g = G*M/R² a = v^2 / r 3. The attempt at a solution I know using g = G*M/R² to find magnitude of the gravitational field. In order to find R using a = v^2 / r; but I dont know how to find a from the graph. Please help! Thanks! Note: I'm not sure if my tried solution is correct or not. Please advise!