How could two observers measure a different speed for the same moving object?

Question

This is more of a science question about motion...

Answer 1

Easy. If you applied this question to a case of 2 independent witnesses reporting a collision or accident that occurred, and both independent reports on witnessed speed of the vehicle in question are grossly different , these are the possible reasons;

1. Angle of observation.
2. Flaws In the processing of recall
3. Lying
4. Ability (Inability) of the witness to accurately calculate visual speed vs actual speed. What may appear very fast may be merely 40 mph.
5. Subjective witness who have other motives beside telling the truth.

The truth is that nobody looks for accidents ready to happen. What an observer does is recounting what he or she can recall in a split second of something witnessed.