Final answer:
At Earth's escape velocity of 11.2 km/s, the length contraction of a 68.2-mm-long spacecraft would be imperceptibly small and essentially zero since this velocity is not a significant fraction of the speed of light.
Step-by-step explanation:
The question addresses the effects of relativistic speeds on the length of objects, specifically a spacecraft reaching Earth's escape velocity of 11.2 km/s. According to Einstein's theory of special relativity, as objects move closer to the speed of light, they experience length contraction as observed from a stationary frame of reference. However, the speed given, 11.2 km/s, is much slower than the speed of light (approximately 300,000 km/s), so the percent decrease in length of the 68.2-mm-long spacecraft traveling at escape velocity would be imperceptibly small and essentially zero for practical purposes. Relativistic effects only become significant at velocities that are a substantial fraction of the speed of light.