Question

Two cars approach each other on a straight and level road. Car A is traveling at 75 km/h, due north and car B is traveling at 45 km/h, due south. Both velocities are measured relative to the ground. What is the velocity of car A relative to an observer in car B?

Answer 1

The velocity of car A relative to an observer in car B is the same as velocity of B relative to A:

$$v=v_A+v_B=75+45=120\text{ km/h}.$$