OK, in a number of episodes they made a point of leaving solar systems under impulse power-and there has been mention of gravitational disruptions if you go to warp "too near a planet",
re: ballistics-the calculations become extremely absurd when you take into account not just trajectory but also gravitational influences, 'quantum flux'(the catch-all for subspace eddies and spacial disturbances in ST) and of course, the simple idea that we are attempting to launch faster than light objects(read:warheads) at an object that is virtually stationary. Put a ping pong ball in the middle of your kitchen table. Make sure the ball has a magnet inside of it. Place at least 2 or 3 other magnets around it. Vary the distance of each magnet, ranging from 1 inch to 6 inches. Now get yet another magnet about the size of a staple. Stand 6 feet away from the edge of the table and make the staple-sized magnet in you hand stick to the ball when you throw it on your ballistic trajectory.Child's play, right? Let me know how it works out.