Math 180 Worksheets 3. Astronaut Bob is standing on a platform 3 meters above the moon's surface and throws a rock directly upward with an initial velocity of 16 m/s. The acceleration due to gravity on the moon's surface is 1.6 m/s?. (a) After how many seconds does the rock reach its highest point? (b) After how many seconds does the rock fall back onto the moon surface? (Assume the platform and the astronaut have moved away after throwing the rock.)