James threw a ball from the roof of a building. The ball fell 3 feet in the first second, 9 feet in next second, and 27 feet in the third second. Which expression represents the distance the ball fell at the nth second?
D=1/2.g.t^2, where D=distance the object has fallen, g=9.81m/sec^2(being the pull of gravity), t=time elapsed in seconds.
