What height does a plane flying at 0.75 c achieve in its own reference frame if it is 1260 m above the ground?

In the scenario described, the plane is traveling at 0.75 times the speed of light (denoted as 0.75 c) and is positioned 1260 meters above the ground. When evaluating this situation, it's essential to understand concepts related to special relativity, specifically concerning how height is perceived in different reference frames.

In the plane's reference frame, it remains at a constant height of 1260 meters above the ground, regardless of its velocity. Height is a measurement that is considered absolute within the object's own reference frame since it measures the distance to the ground from the plane's perspective. Consequently, as long as the plane does not change its vertical position relative to the ground, its height remains unchanged.

While the speed of the plane relative to an observer on the ground may influence other measurements such as time and length due to relativistic effects, it does not affect the measurement of height in the plane's own frame. Therefore, the answer that correctly represents the height of the plane in its own reference frame is indeed 1260 meters.