题目

阅读理解 Every week in China, millions of people will sit in front oftheir TVs watching teenagers compete for the title Character Hero, which is a Chinese­stylespelling bee (拼写大赛).In this challenge, young competitors must write Chinese characters by hand. To preparefor the competition, the competitors usually spend months studying dictionaries. Perhaps the show's popularity should not be a surprise. Alongwith gunpowder and paper, many Chinese people consider the creation of Chinese calligraphy(书法) to be one of their primary contributions.Unfortunately, all over the country, Ch总质量为M的列车，沿水平轨道匀速地前进，其末节车厢质量为m，中途某时刻脱节，脱节后的列车仍以原来的牵引力继续前进。从脱节开始到司机发觉，列车已从脱节位置向前行驶L的距离。司机立即关闭油门，撤去牵引力。设运动时阻力与车重成正比。当脱节车厢和列车这两部分都停止运动时，它们的距离是多少？