1. The problem statement, all variables and given/known data Two ships are traveling parallel to each other in opposite directions with seed v1 and v2. One ship fire on the other. At what angle should the gun be aimed at the target ship in order to make a hit if the shot is fired at the instant when both vessels are on the straight line perpendicular to their course? The shell velocity v0 is assumed constant. 2. Relevant equations 3. The attempt at a solution The answer in text is : theta = arccos( (v1 +v2)/v0) The book doesn't have an explanation, and I am having trouble just being able to draw the situation. I don't understand what it means when the problem says " when both vessels are on the strait line perpendicular to their course."