a friend of mine asked if i could help him work out some equations for a (fairly) long range projectile, to go no farther than 2 miles or so. i have everything reasonably worked out except for acceleration due to air resistance. i'm using the equation from this thread to calculade Fd, and Cd=.295, rho=1.22752kg/m^3, A=pi.2^2m^2, v=240m/s, firing an object with a mass of .23kg. (Cd and rho both came from the Nasa website) I did the calculations and got an estimated acceleration of about (-)5698 m/s^2, which obviously cannot be right. I was also wondering if there is any way to get a more accurate velocity by factoring in acceleration of gravity and air resistance. I'd assume it'll take some nasty algebra/calculus, but i can't figure it out on my own. any help is greatly appreciated.