If a hole were dug through the center of a planet and a ball dropped
into the hole, which of the following best describes the motion that the
ball would undergo? Assume the ball is indestructible and the planet is
a perfect sphere.
(A) It would continuously gain speed and eventually escape the
gravitational pull of the planet.
(B) It would fall to the center of the planet and get stuck there
because gravity is always pulling things toward the center of
the planet.
(C) It would fall to the other end of the hole, come to a momentary
stop, fall back to the starting location, and then repeat this
back-and-forth motion indefinitely.
(D) None of the above is correct.