The residents of a small planet have bored a hole straight through its center as part of a communications system. The hole has been filled with a tube and the air has been pumped out of the tube to virtually eliminate friction. Messages are passed back and forth by dropping packets through the tube. The planet has a density of 4120kg/m^3, and it has a radius of R= 5.67E+6 m. What is the speed of the message packet as it passes a point a distance of .420R from the center of the planet?
How long does it take for a message to pass from one side of the planet to the other?
The Attempt at a Solution
I first found the mass in equation one. Then I thought .420R was x, the radius is A and, that is as far as I got with that.
Am I wrong so far?