A car travels north at 30 m/s for one half hour. It then travels south at 40 m/s for 15 minutes. The total distance the car has traveled and its displacement are:
1) 18 km; 18 km S.
2) 36 km; 36 km S.
3) 36 km; 36 km N.
4) 90 km; 18 km N.
5) 90 km; 36 km N.
Answer: 4