题目

Last year I ruined my summer vacation by bringing along a modern convenience that was too convenient for my own good: the iPad. Instead of looking at nature, I checked my e-mail. Instead of paddling a small boat, I followed my Twitter feed（推特简讯）. Instead of reading great novels, I stuck to reading four newspapers each morning. I was behaving as if I were still in the office. My body was on vacation, but my head wasn’t.So this year I made up my mind to try something different: withdrawal（退出）from the Internet. I knew it wouldn’t be easy, since I’m bad at self-control.? 11．如图所示，质量m1=3kg的滑块C（可视为质点）放置于光滑的平台上，与一处于自然长度的弹簧接触但不相连，弹簧另一端固定在竖直墙壁上．平台右侧的水平地面上紧靠平台依次排放着两块木板A、B．已知木板A、B的长度均为L=5m，质量均为m2=1.5kg，木板A、B上表面与平台相平，木板A与平台和木板B均接触但不粘连．滑块C与木板A、B间的动摩擦因数为μ1=0.3，木板A、B与地面间的动摩擦因数μ2=0.1．现用一水平向左的力作用于滑块C上，将弹簧从原长开始缓慢地压缩一段距离，然后将滑块C由静止释放，当滑块C刚滑上木板A时，滑块C的速度为7m/s．设最大静摩擦力与滑动摩擦力大小相等，取g=10m/s2．求：（1）弹簧的最大弹性势能；（2）滑块C刚滑上木板A时，木板A、B及滑块C的加速度；（3）从滑块C滑上木板A到整个系统停止运动所需的时间．