在光滑绝缘的水平桌面上，存在水平向右的电场，电场线如图中实线_爱下问搜题

搜题请搜索小程序“爱下问搜题”

问题选择题

在光滑绝缘的水平桌面上，存在水平向右的电场，电场线如图中实线所示．一带电的小球以一定的初速度从桌面上的A点开始运动，到C点时，突然受到一个外加的水平恒力F作用而继续运动，到B点，其运动轨迹如图中虚线所示．v表示粒子在C点的速度，则下列判断中正确的是（　　）

A．恒力F的方向可能水平向左

B．恒力F的方向可能与v的方向相反

C．在A、B两点小球的速率不可能相等

D．小球在A点的电势能比在B点的电势能小

答案

A、由AC段轨迹：根据曲线运动物体所受的合力指向轨迹的内侧可知，电场力方向水平向右．根据AC段轨迹弯曲方向判断可知：恒力F的方向可能水平向左，而且F大于电场力．故A正确．

B、若恒力F的方向与v的方向相反，则小球所受的合力方向指向右下方，不可能沿AC曲线运动，故恒力F的方向不可能与v的方向相反．故B错误．

C、整个过程中，电场力做正功，若恒力做负功，两者功的大小相等，总功为零，根据动能定理得知在A、B两点小球的速率可能相等．故C错误．

D、从A到C过程中，电场力做正功，电势能减小，则小球在A点的电势能比在B点的电势能大．故D错误．

故选A

翻译题

“Who did this?” asked my teacher. Thirty children tried to think about not only what they had done, but also what our teacher         have found out.
“Who did this?” she asked         . She never became         , but she was this time. She help up a piece of broken glass and asked, “Who broke the window?”
“Oh, no,” I thought. I was the one who broke the window. I did not do it on purpose (故意地). It was caused by a         throw （投，掷）of a baseball. But         did it have to be me?
If I admitted （承认）it, I would        into a lot of trouble. How would I be able to      a big window like that? I didn’t want to raise my hand.         , something much stronger than me pulled me up. “I did it.” Then I kept quiet.         was hard enough to say what I felt.
My teacher went to the           and took down a book. She then began walking to my desk. I         she was going to punish （惩罚）me.
“I know           you like birds,” she said as she stood looking down        my face. “Here is a book about birds. It is         now. You will not be punished. But remember, it’s only for your honesty.”
I couldn’t believe it! I wasn’t punished and I was getting a book. I had been saving up all my money to buy       .

综合

读地球内部结构简图，回答下列问题。

(1)写出图中字母表示的地球内部圈层的名称：

A ，B₁ ，

B₂ ，D ，

E ，F 。

(2)C是层，这里可能是的主要发源地之一。

(3)岩石圈的范围是指。(用字母表示)