Hi, My problem is very simple... but yet it rises some doubt. I am calculating how long a projectile goes taking into account air drag. For the displacement I have the following formula: x=(v0+Vterminal)/k*(1-e^(-kt)-Vterminal*t+x0 where k is the air drag coefficient I know that this formula already includes both components of the velocity, thus it should give the correct displacement. The equation states that my initial velocity is: 31.1m/s The X component of the velocity is: 15.55m/s. Which value of the velocity should i insert on the equation? I have done the calculations with both and the results differed by very little, hence my confusion. Appreciate the help, thanks. R.