2009年第26届全国中学生物理竞赛复赛中的第六题是一道涉及狭义相对论的问题,这里我们给出几种解法,这些解法都程度不同的需要应用电动力学中相对论四维时空理论的知识和结论。由此可见,电动力学的学习对我们未来的中学物理教师以及有志参加物理竞赛的中学生来说是具有重要意义 The 26th issue of the 26th National Junior High School Physics Contest in 2009 is a question related to the special theory of relativity. Here we give some solutions, all of which have different degrees of need to apply the knowledge and conclusions of the four-dimensional space-time theory of relativity in electrodynamics . Thus it can be seen that the study of electrodynamics is of great importance to our future high school physics teachers as well as to middle school students interested in participating in the physical competition