题干

如图甲所示,两个点电荷Q1、Q2固定在x轴上距离为L的两点,其中Q1带正电荷位于原点O,a、b是它们的连线延长线上的两点,其中b点与O点相距3L.现有一带正电的粒子q以一定的初速度沿x轴从a点开始经b点向远处运动(粒子只受电场力作用),设粒子经过a,b两点时的速度分别为va、vb,其速度随坐标x变化的图象如图乙所示,则以下判断正确的是(   )

A:Q2带负电且电荷量小于Q1

B:b点的场强一定为零

C:a点的电势比b点的电势高

D:粒子在a点的电势能比b点的电势能大

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答案(点此获取答案解析)

A,B

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请先阅读下面短文,掌握其大意,然后根据短文内容从下面方框内的七个选项中,选择五个还原到文中,使短文意思通顺、结构完整,并在答题卡上将其序号涂黑。

Humans’ Greatest Achievements

     The Earth is 4.5 billion years old, but the human race has lived on it for just 200,000 years. In that short time, we have achieved some amazing things.

    ____ The list is almost endless. The invention of the airplane has changed our lives. The discovery of antibiotics (抗生素) has saved the lives of millions of people. Can you imagine living without electricity? What about the printing press (印刷术)? Without the printing press, you wouldn’t be reading this. In the last 50 years, there have been great achievements in communication, such as radio, TV, computers, the Internet, and smartphones (智能手机). ____

    What about the arts? The arts have brought pleasure to many people, but are the Beatles and Bach more important than antibiotics? ____

Finally, we must not forget humans' early achievements. ____ We can't imagine modern life without cooked food and cars.

    What are humans' greatest achievements? To answer the question, we need to decide what we mean by “great”. ____ Or is it just something that makes us say “Wow,” like the Great Wall? What do you think?

A. Do you think it is difficult to have great achievements?

B. Is it something that makes us rich or happy or save lives?

C. We enjoy these things every day because they are free to use.

D. They used fire for cooking and heating and invented the wheel.

E. Many of humans' great achievements are in science and technology.

F. And is Mickey Mouse as important an achievement as going to space?

G. We could probably live without them, but life wouldn’t be as interesting.