An observer measures the length of an object. In which of the following cases is the measured length at a minimum?

Question

Choose one answer.
a. The observer and the object move with the same speed v in the same direction.
b. The observer and the object move with the same speed v in the opposite direction.
c. The observer and the object move with the same speed v in perpendicular directions.
d. The observer moves at an angle 30° to the direction of the object, but both move with the same speed.

Answer 1

Case (b), which has the highest relative velocity (2v), and the greatest relativistic length contraction.