
Michael F. answered 09/12/19
Licensed NC High School Physics teacher, AP & honors.
Joe is right on ... you can separate the motion in the x direction (horizontal) and the y direction (vertical) and only the latter is affected by gravity... the speed in the x-direction remains constant (neglecting air resistance--which a real artillery crew could not do!) and so the distance is just the horizontal velocity multiplied by the time of flight. .