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问题 计算题

质量为m的物体以初动能100J从倾角为θ的斜面底端A点沿斜面匀变速滑行到斜面上B点时，物体的动能减少80J，机械能减少32 J，则当物体回到A点时的动能为多少？

答案

解：设由A点到B点经过的位移为s1，运动到C点的速度减为0，由B点到C点的位移为 s2

对于由A点到B点的过程运用动能定理可得-mgs1sinθ-μmgcosθs1=-80 J

且μmgcosθs1=32 J

对于由B点到C点的过程运用动能定理可得-mgs2sinθ-μmgcosθs2=-20 J

所以s1=4s2

所以μmgcosθs2=

所以上升过程中摩擦力做的总功为-40 J

下降过程摩擦力大小不变，总位移大小相同，所以下降的过程中摩擦力做功也为-40 J

对全过程利用动能定理即可解得物体回到出发点时的动能为20 J

完形填空

完形填空（二）（本题共15小题，满分30分）

阅读下面短文，根据文意，将方框内所给的词或短语的适当形式填入相应的空白处，使短文的意思完整。（每个词只能使用一次）（本题共十小题，每小题2分，满分20分）

We all need a healthy environment, but we produce waste every day and it__小题1:__ our environment. Though we are young, we can still do something to help. In fact, even the simplest _小题2:__activities can make a real difference to the environment. Here are some ideas for you.

Reduce means “use less”. Don’t waste things. This __小题3:__money and reduces pollution and waste going into the environment. Before we buy something new, think ___小题4:____it is really necessary—or maybe the old one will be just as good! When we do buy things, choose local products if __小题5:_____ and try not to buy too many things from abroad.

Reuse means “use again”. Use things for as long as possible. When we buy things, make sure that they __小题6:__ a long time. We should look after them__小题7:_ they will last and we should repair them if we can instead of  throwing them away and buying new ones. Don’t use a paper cup or a paper bag. It’s better to use a china cup and a lunch box because you can use them __小题8:__.

Recycle means “change things into something else”. Although it takes ___小题9:_ to change something into something else, it’s better than throwing things away or burning them. Find out what can be recycled in your_小题10:__ and take part in recycling programmes. We should also buy products made from recycled materials, such as recycled paper, to help save trees.
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单项选择题

法洛四联症包括下列哪项畸形（）

A.肺动脉狭窄

B.室间隔缺损

C.主动脉骑跨

D.右心室肥厚

E.以上都是
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