in this question change v=v2-v1: a car traveling at 15m/s [N] executes a gradual turn, so that it then moves at 18m/s[E]. Calcue change in veloctiy. but in this question change v= v2+v1: A plane's velocity changes from 200km/h[N] to 300 km/h [N 30 W]. Find the plane's change on velocity. How do i know when to use which formula?