Suppose that, while lying on a beach near the equator watching the Sun set over a calm ocean, you start a stopwatch just as the top of the Sun disappears. You then stand, elevating your eyes by a height , and stop the watch when the top of the Sun again disappears. If the elapsed time is , what is the radius of the earth?
I drew a diagram but I can't get anywhere with it! No extra information is given to aid the question.