Q. For a spherical celestial object of radius R, acceleration due to gravity g at a distance x from the center of the object is g = g0R2/x2, where g0 is the acceleration due to gravity at the object's surface and x > R. For the moon, take g0 = 1.63 m/s2 and R = 3200 km. If a rock is released from rest at a height of 3R above lunar surface, with what speed does rock impact the moon? Hint: Its acceleration is a function of position and increases as the object falls. So do not use constant acceleration free-fall equations, but go back to basics.