Open and Solved Elementary Questions in Astronomy

Some school scientific problems are posed: 1) Let's consider a tunnel getting from one side to the other of a planet and passing through the planet center. An object is dropped into the tunnel. Is the object oscillating about the center as a pendulum? What happens if the tunnel gets from a side to another side of the planet but doesn't pass through the planet center, would the midpoint of the tunnel play a similar role as the planet center? How will Coriolis force influence this? 2) Is it possible to accelerate a photon (or another particle traveling at, let's say, 0.999c) and thus to get a speed greater than c?