题干

如图所示,质量为58g的网球,以v1=40m/s的速度水平飞来,运动员以60m/s的速度反拍击回的过程中,网球的动量变化为(   )

A:大小为1.16kg•m/s,方向v1方向相同

B:大小为1.16kg•m/s,方向v1方向相反

C:大小为5.8kg•m/s,方向v1方向相同

D:大小为5.8kg•m/s,方向v1方向相反

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D

同类题3

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储蓄人生

雁鸣

    ①人们在吃饱穿暖之后,知道了要储蓄,以便在需要的时候支取它,借助它走出困境。每当我清点一张张金额不大但令人鼓舞的存单时,心里就有一种感悟:人生,不也是储蓄吗?

    ②一个人呱呱坠地,便开始储蓄真情。这一储蓄会伴随他或她走过一生。他们所储蓄的,是一种血肉相连的情感,是一笔超越时空的财富,无论离得多远、隔得多久,都可以随意支取和享用它们。有了亲情这笔储蓄,即使在物质上很贫困,精神上却是富有的;而不懂或丢失了亲情的储蓄,无异于泯灭了本性和良心。

    ③友情,也是人生一笔受益匪浅的储蓄。这储蓄,是患难之中的倾囊相助,是错误路上的逆耳忠言,是跌倒时一把真诚的搀扶,是痛苦时抹去泪水的一缕春风。真正的友情储蓄,不是可以单向支取的,而要通过双方的积累加重其分量,任何带功利性的友情储蓄,不仅得不到利息,而且连本钱都会丧失殆尽

    ④爱情是一种幸福而艰苦的储蓄。一对陌路相遇的男女,婚前相恋固然需要执着的储蓄,而要在一个屋檐下应对几十年的风风雨雨,又需要储蓄多少和谐、多少默契、多少理解、多少扶助啊!这绝不是靠花前月下、甜言蜜语的一次性投入可以解决问题的。享用这笔储蓄如享用清冷中的一盆火、泥泞中的一缕阳光、患病时的一句深情的话语、彷徨时的一番温柔鼓励。爱情的常爱常新,需要月月储蓄、日日积攒。

    ⑤学识的储蓄要锲而不舍。一个人从幼小到成熟的过程,就是不断地储蓄知识的过程。接受小学、中学、大学乃至更高的教育,这仅仅是储蓄知识的一个方面,重要的在于刻苦勤勉,日积月累,不断地充实和更新知识、坚持活到老学到老、“储蓄”到老。

    ⑥人生需要储蓄的东西很多。储蓄人生,就是要储蓄人生中那些最宝贵、最难忘、最精致的部分,储蓄一切至真至善至美。一个人懂得储蓄什么,并知道怎样去储蓄,实在是一种智慧与幸运。

同类题4

阅读理解

    I recently posted a picture on Facebook from the movie Mad Max, a film where two groups race through the desert in steampunk vehicles, and wrote, “Actual picture of my way to work today.” It was meant to be a joke because of the sandstorms in Beijing, but one of my friends from back home thought it was real.

    I couldn't imagine how they could think that is actually what China is like. China has so many more conveniences and advantages than the West, and many of my friends agree. “I don't know how I will be able to deal when I go back home,” said a friend who is about to end her gap year in Beijing. “I've become so spoiled in China.”

    China seems to be leading the way in innovation(创新) and convenience for daily life. Back home I could never shop, pull out my phone and scan a QR code to pay.

    There have been rumors of starting bike sharing in my hometown for years with little success while bike sharing suddenly appeared in Beijing overnight. I just step outside and scan a code, and I am on my way.

    Going out to eat with a group of friends back home was troublesome for both the group and the servers. Splitting bills and swiping(刷) 10 different cards or making change for each person in the group can be a pain. But with China's WeChat, you can quickly send your friends your part of the bill.

    The list goes on…

    When I first arrived in Beijing, I was dead set on leaving in a month. That month has come and gone. Now, when someone asks me when I'm coming back, I think to myself, “Who knows?”

    While my friends think I am riding through the desert on a motorbike, I am actually taking a Didi for what is the equivalent of $5 in the US.

    With all the conveniences and technology here, I may never want to go back.