题目

阅读理解，阅读下列短文，从每小题所给的A、B、C、D四个选项中选出最佳选项。      Many people say that they are working too many hours. They don't have enough time to relax or to stay with their family.     Work hours are different from one country to another. In France, people spend about 1,646 hours a year at work. In Japan, however, people work about 2,159 hours a year. That means a Japanese worker works 513 more hours a year than a French worker.     Why do people work so many hours? Some people work extra hours because they want to make more 如图所示，两块相同平板P1、P2置于光滑水平面上，质量均为m。P2的右端固定一轻质弹簧，弹簧的自由端恰好在P2的左端A点。物体P置于P1的最右端．质量为2m且可以看作质点。P1与P以共同速度v0向右运动，与静止的P2发生碰撞，碰撞时间极短，碰撞后P1与P2粘连在一起，P压缩弹簧后被弹回并停在A点(弹簧始终在弹性限度内)。P与P2之间的动摩擦因数为，求     ①P1、P2刚碰完时的共同速度v1和P的最终速度v2；     ②此过程中弹簧最大压缩量x。