On a planet with no atmosphere and a mass 3 that of Earth's, a 1235 kg rock falls off of a cliff. Beginning at an arbitrary time during free fall, the resulting vertical velocity of the rock as a function of time is shown in the graph. Velocity (m/s) 0 -10- -20- -30- -40- -50- 0 1 2 3 4 5 Time (s) 6 7 8 9 1 Determine the radius of this planet in terms of Earth radii, RE, if the planet has the mass of the Earth. 3