Answer:
It is due to relative motion.
Explanation:
Relative motion is the motion of a body relative to another body as observed from a point of reference.
For example, a student on a moving school bus. For an observer on the same bus it will appear that the student is not moving because there’s no relative motion between the student in the moving bus and the observer since they’re both moving at the same speed. However, if the observer was standing by a bus stop watching the bus pass by, the student in the moving bus will appear to be moving too. The point of reference here is the position of the observer. So, the motion of a body ‘A’ with respect to another body ‘B’ is the motion of ‘A’ as observed from ‘B’.
For the question above, let's assume the faster bus is moving at 50km/h and the slower bus at 20km/h
I. When the two buses are moving in the same direction,
The resultant speed = speed of the faster car – speed of the slower car = 50-20 = 30km/h. For an observer in the slower bus, the faster overtaking bus will be moving at 30km/h.
II. When the buses are moving in opposite direction,
The resultant speed = speed of faster car + speed of slower car = 50+20 = 70km/h. For an observer in the slower bus, the faster bus will be moving at 70km/h.
That is why the speed of vehicles appears slower during overtaking and faster when they are coming from the opposite direction.
