题目

I was driving home the other day on a sunny afternoon. I had a smile on my face as I sang along to the songs on the radio. It was a beautiful day that I felt full of happiness. My good mood ended, however, when the radio station took a news break between songs. Then suddenly I found myself listening to yet another story of a rich famous man who had broken the law. I shook my head as I came to a red traffic light. As I pulled to a stop I noticed four leather-jacketed bikers. They were standing in the middle of the road with two on either side of the light. They looked rough and dangerou火车在铁轨上行驶时，由于在铁轨接头处受到撞击而上下振动.如防震弹簧每受104N的力将被压缩20mm，而每个弹簧的实际负荷为5.0×103kg.问车速多大时，弹簧压缩得最强烈?(设铁轨长为12.5m,g=10m/s2)