Final answer:
The speed of an airplane is determined by its frame of reference, which is the perspective from which its motion is observed.
Step-by-step explanation:
The factor that determines how fast an airplane is moving is its frame of reference. Frame of reference refers to the perspective or point of view from which an object's motion is observed. The speed of an airplane may vary depending on the frame of reference of the observer.
For example, if two airplanes are flying side by side at the same speed, an observer inside one airplane will perceive the other airplane as stationary or moving slowly when compared to their own frame of reference. However, an observer on the ground will see both airplanes moving at the same speed.
Therefore, it is important to consider the frame of reference when discussing the speed or motion of an airplane.
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