题干

如图,MN是负点电荷电场中的一条电场线,一带正电的粒子(不计重力)从a到b穿越这条电场线的轨迹如图中虚线所示.下列结论正确的是(   )

A:带电粒子在a点时的加速度小于于在b点时的加速度

B:带电粒子在a点时的电势能大于在b点时的电势能

C:带电粒子从a到b运动的过程中动能逐渐减小

D:负点电荷一定位于N点右侧

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C

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    Five years ago, when I taught art at a school in Seattle, I used Tinkertoys as a test at the beginning of a term to find out something about my students. I put a small set of Tinkertoys in front of each student, and said: “Make something out of the Tinkertoys. You have 45 minutes today - and 45minutes each day for the rest of the week.”

    A few students hesitated to start. They waited to see the rest of the class would do. Several others checked the instructions and made something according to one of the model plans provided. Another group built something out of their own imaginations.

    Once I had a boy who worked experimentally with Tinkertoys in his free time. His constructions filled a shelf in the art classroom and a good part of his bedroom at home. I was delighted at the presence of such a student. Here was an exceptionally creative mind at work. His presence meant that I had an unexpected teaching assistant in class whose creativity would infect(感染)other students.

    Encouraging this kind of thinking has a downside. I ran the risk of losing those students who had a different style of thinking. Without fail one would declare, “But I'm just not creative.”

    “Do you dream at night when you're asleep?”

    “Oh, sure.”

    “So tell me one of your most interesting dreams.” The student would tell something wildly imaginative. Flying in the sky or in a time machine or growing three heads. “That's pretty creative. Who does that for you? “

    “Nobody. I do it.”

    “Really-at night, when you're asleep?”

    “Sure.”

    “Try doing it in the daytime, in class, okay?”