问题 计算题

静电喷漆技术具有效率高,浪费少,质量好,有利于工人健康等优点,其装置示意图如图所示。A、B两块平行金属板,间距d=0.30m,两板间有方向由B指向A,电场强度E=1.0×103N/C的匀强电场,在A板的中央放置一个安全接地的静电油漆喷枪P,油漆喷枪的半圆形喷嘴可向各个方向均匀地喷出带电油漆微粒,油漆微粒的质量m=2.0×1015kg,电荷量q=-2.0×10-16 C,喷出的初速度v0=2.0 m/s,油漆微粒最后都落在金属板B上。微粒所受重力和空气阻力及微粒之间的相互作用力均忽略,求:

(1)向粒落在B板上的动能;

(2)微粒从离开喷枪后剑达B板所需的最短时间;

(3)微粒最后落在B板上所形成图形的面积。

答案

解:(1)据动能定理,电场力对每个微粒做功W=Ekt-Ek0=qEd

微粒打在B板上时的动能Ekt=W+Ek0=

代入数据解得:Ekt=6.4×10-14 J

(2)微粒初速度方向垂直于极板时,到达B板时间最短,到达B板时速度为vt,有

,可得vt=8.0 m/s

由于微粒在两极板间做匀变速运动,即

可解得t=0.06 s

(3)由于喷枪喷出的油漆微粒是向各个方向,因此微粒落在B板上所形成的图形是圆形。对于喷枪沿垂直电场方向喷出的油漆微粒,在电场中做抛物线运动,根据牛顿第二定律,油漆颗粒沿电场方向运动的加速度

运动的位移

油漆颗粒沿垂直于电场方向做匀速运动,运动的位移即为落在B板上圆周的半径R=v0t1

微粒最后落在B板上所形成的圆面积S=πR

联立以上各式,得

代入数据解得S=7.5×10-2 m2

单项选择题 A1/A2型题
阅读理解

Poverty today is a major global issue. Although there are all kinds of definitions used to explain it, in simple words, it means the inability of a person to even get his basic needs of food, shelter, clothing, safe drinking water, health and education. Poverty can be found in each and every corner of the world, although the causes may differ from country to country. Given below are the main causes of poverty in the world today.

Overpopulation is one of the main causes behind the threatening of poverty on an individual level as well as a social level. This is simple math. If there are more mouths to feed and less income, definitely much will remain poor.

Another theory which is used as an explanation for poverty is lack of education. If you look at any of the underdeveloped countries, you will find that the level of education there is very low. Lack of education means lack of employment opportunities, thus leading to unemployment coupled with poverty in the future.

Moving away from one’s own homeland to another city or country in search of employment leads to poverty too. It may take these people a lot of time to find jobs. Meanwhile they live in bad conditions. The cost of living in the city or country is most of the time too high for them.

There may be other causes of poverty like the change in business. For example, in America, a couple of decades ago, heavy industry flourished, which employed a lot of African-American people. But now, the focus is more on information technology and health care, both of which employ only skilled and trained people. This has led to unemployment among African-Americans.

Poverty has many ill effects on society. That’s why steps should be taken to get rid of it!

小题1:What’s the meaning of the underlined word “flourished” in Paragraph 5?

(No more than 5 words)

小题2:Why is overpopulation a cause of poverty today?  (No more than12 words)

小题3:What’s the situation of education in underdeveloped countries?  (No more than 8 words)

小题4:What does the passage mainly talk about?   (No more than 10 words)

小题5:In your opinion, what’s the most significant cause of poverty today? Please give your reason.  (No more than 25 words)