1. The problem statement, all variables and given/known data if theres a plane traveling north at 200 m/s and then travel south at 200 m/s then its change in velocity is 400 m/s south. 2. Relevant equations 3. The attempt at a solution okay so the answer is 400 m/s south. however, i don't understand why the change is 400, and not 0 or just 200? i see the new direction is south. is there an equation for problems like these? maybe you could make up another example with the answer included so i can see this better. thanks.