这个是对的，假设匀速，也只有这样假设

来源: 黄处长于 2009-02-01 21:42:59 [博客] [旧帖] [给我悄悄话] 本文已被阅读：次

WENXUECITY.COM does not represent or guarantee the truthfulness, accuracy, or reliability of any of communications posted by other users.