How fast must a plane travel relative to the ground for relativity effects to be observed?

To determine the speed at which significant relativity effects can be observed, it is crucial to consider the factors governing relativistic physics. The effects of relativity become more pronounced as an object moves at speeds close to the speed of light. A common threshold for observable relativistic effects in practice is around 10% of the speed of light, which is approximately 3 x 10^7 m/s.

In the context of the provided question, the speed associated with option B, 2.9 x 10^6 m/s, represents a significant fraction of the speed of sound and is approximately 10% of the speed of light. At this speed, relativistic effects, such as time dilation and length contraction, may begin to be notable, especially when measured using sensitive instruments or in experiments designed to detect these phenomena.

Observing relativity effects requires not just high speeds, but a substantial proportion of the speed of light (around 30,000,000 m/s). The other options relate to speeds that are either too low in context or do not demonstrate the comparability to significant effects necessary for relativity to be observable comprehensively. Thus, the selection of 2.9 x 10^6 m/s aligns well with the