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问题 选择题

水平面上有两个质量相等的物体a和b，它们分别在水平推力F1和F2作用下开始运动，分别运动一段时间后撤去推力，两个物体都将运动一段时间后停下.物体的v-t图线如图5-1-4所示，图中线段AB∥CD.则以下说法正确的是(    )

①水平推力的大小F1>F2

②水平推力的大小F1＜F2

③a所受摩擦力的冲量大于b所受摩擦力的冲量

④a所受摩擦力的冲量小于b所受摩擦力的冲量

图5-1-4

A.①③             B.①④              C.②③               D.②④

答案

答案：B

根据v-t图象,由于AB∥CD,可见两物体与水平面间的动摩擦因数相同,设为u,在a、b加速运动过程中,由牛顿第二定律知,>                      ①

由于ma=mb,得F1>F2.在a、b两物体各自全过程中,由动量定理知,

F1ta-μmagta总="0                                                              " ②

F2tb-μmbgtb总="0                                      "                         ③

由v-t图象得ta总<tb总                                                          ④

根据②③④式得F1ta<F2tb,即推力F1的冲量小于推力F2的冲量,容易知a所受摩擦力的冲量小于b所受摩擦力的冲量.选项B正确.

填空题

阅读下面材料，在空白处填入适当的内容（1个单词）或括号内单词的正确形式。    

Chengdu has dozens of new millionaires, Asia’s biggest building, and fancy new hotels. But for tourists like me, pandas are its top（61）(attract).

So it was a great honour to be invited backstage at the not-for-profit Panda Base, where ticket money helps pay for research, I（62）（arrow）to get up close to these cute animals at the 600-acre centre. From tomorrow, I will be their UK ambassador. The title will be（63）(official) given to me at a ceremony in London.But my connection with pandas goes back （64）my days on a TV show in the mid-1980s,（65）I was the first Western TV reporter（66）(permit) to film a special unit caring for pandas rescued from starvation in the wild. My ambassadorial duties will include（67）(introduce) British visitors to the 120-plus pandas at Chengdu and others at a research in the misty mountains of Bifengxia.

On mu recent visit, I help a lively three-month-old twin that had been rejected by（68）(it) mother. The nursery team switches him every few（69）(day) with his sister so that while one is being bottle-fed,（70）other is with mum-she never suspects.

68（）
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单项选择题

消化性溃疡最主要症状是（）

A.嗳气、反酸、恶心

B.呕吐

C.无规律性上腹痛

D.节律性上腹痛

E.无规律性下腹痛
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