题干

“星跳水立方”节目中,某明星从跳板处由静止往下跳的过程中(运动过程中某明星可视为质点),其速度﹣时间图像如图所示,则下列说法正确的是(   )

A:跳板距离水面的高度为7.5m

B:该明星入水前处于失重状态,入水后处于超重状态

C:1s末该明星的速度方向发生改变

D:该明星在整个下跳过程中的平均速度是7.5m/s

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答案(点此获取答案解析)

B

同类题2

   Here is a 2-way student exchange. Fred, 19 , spent last year in Germany with George’s family. In turn, George’s son Mike spent a year in Fred’s home in America.
   Fred knew little German when he arrived. But after 2 months of studying, the language became easy for him. School was very different from what he had looked forward to and it was much harder. Students stood up politely when the teacher came into the room. They took 14 subjects while American students usually took 6 in the US.
   Family life, too, was different. The father’s word was the law(法律) . All the children had to do their activities with their family. Fred also missed having a car. In Germany, you should walk to go out to have a good time.
   At the same time, in America, Mike was forming his own ideas. He says,’ American schools are too easy for our level but I have to say that I like it a lot in Germany , we do nothing except study. Here we take part in many other activities.

Differences between American school life and German school life
ItemsAmerican studentsGerman students
Class rulesThey don’t have to stand up when their teacher come inThey have to ____  up and show respect(尊敬) to their ____ 
____  lifeThey do their own things alone.They have to listen to their ____ 
School ____ They have six and they are very easy for themThey have 14, but the lessons are much more ____ 
Going outThey can____  carsThey have to ____  all the way
School activitiesThey have ____  other activitiesThey have to ____  hard all the time.