If the rail gun works by causing a constant acceleration to a projectile that starts at velocity zero, then the equations for gravitational acceleration will work. The given distance equals gt(squared)/2 and the given speed equals gt, (Time t in seconds and acceleration g in m/sec(squared), and the given units for distance and speed.) So solve those two equations and you would have your answer for both g and t. (I got 7.5 ten-thousandths of a second for time, and 2.667 million meters per second-squared for the acceleration.) The reason this works can be found in any book on elementary (one-variable) integral calculus, or from a tutor.
