Answer:
10 km south
Explanation:
The two displacements of the car are vectors, so they have a magnitude and a direction.
The first displacement is 20 km north.
The second displacement is 30 km south.
Since the two displacements are along the same direction (north-south), we can calculate their resultant simply adding them, but taking one of the two with a negative sign (because they are opposite). If we take south as positive direction, and north as negative direction, the resultant displacement becomes
\(D=-20 km +30 km=+10 km\)
and since it has positive sign, the direction is south.
