题干

如图所示,倾角为37o的粗糙斜面固定在水平地面上,斜面上放置质量均为1kg的A、B两物体,A、B之间有一劲度系数很大的轻质弹簧,弹簧与A栓连,与B接触但不栓连,初始弹簧被锁定,弹性势能为4J,A、B恰好静止在斜面上,物体与斜面间的最大静摩擦力与滑动摩擦力相等,B与斜面间的动摩擦因数是A的2倍,现解除弹簧锁定,A、B在极短的时间内被弹簧弹开,求:

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I was just outof college, only three days into a graduate (研究生)year in England,and I was pulling a heavy bag and suitcase(箱子)through the London Underground. I was also crying out of control.

   The day before yesterday, my uncle told me never to speak to him, his wife, or my two cousins again. Earlier,  I made a joke. I didn't mean to hurt my aunt's feelings, but it did.I spent the evening in an ugly blue telephone booth (电话亭). crying as I spoke to a family friend who lived in England.

   When I left the phone booth, I went back to a silent house with three closed bedroom doors. In the morning, I heard everyone get up and leave for work and school. I wrote a note to say sorry and pulled my bags to the train station. When I got into London, I had to take the underground to Angel Station to get to my family friend's house.

    I was familiar with the underground, but at the time, it was just endless white tiles(瓷砖).Coming to England seemed like a bad decision. Crying yet again, I tried to lift my suitcase up the stairs.

   When I was trying hard to walk forward, there were hands. Each time I faced another group of steps,a hand would lift the suitcase. At the top of the steps, the hand would let go, and I'd pull the suitcase to the next group. And just as I wanted to try again,another hand would appear.

   It happenedseveral times. I never looked up, because I couldn't stop crying.Each hand looked different, and many different people helped me, without asking or saying anything. I couldn't look up. I wasn't able to say thank you.

   I went on to have anamazing year studying in England, but that was the last time I saw or spoke to any of my uncle's family. Yet when I think about that terrible loss in 2008, I remember those strangers' hands. They were there when I needed them, and even now, they help me out of the sadness of that memory. I think of them as I ride the underground in Washington D. C. today, and I watch the citizens and tourists to offer hands at any time.