The small spherical planet called "Glob" has a mass of 7.20 108 kg and a radius of 6.20 104 m. An astronaut on the surface of Glob throws a rock straight up. The rock reaches a maximum height of 2.10 x 10 m above the surface of the planet before it falls back down. What was the initial speed of the rock (in m/s) as it left the astronaut's hand? (Glob has no atmosphere, so no energy is lost to air friction.) G = 6.67 10-Nm/kg.