问题 选择题

如图所示,实线为不知方向的三条电场线,从电场中M点以相同速度飞出a、b两个带电粒子,运动轨迹如图中虚线所示,不计粒子的重力。则

A.a、b一定是同性电荷的两个带电粒子

B.沿M—P轨迹方向电势将降低,沿M—N轨迹方向电势将升高

C.a粒子的加速度将减小,b粒子的加速度将增加

D.a粒子的电势能增加,b粒子的电势能减小

答案

答案:C

题目分析:物体做曲线运动,所受力的方向指向轨道的内侧,所以能判断a、b一定带异种电荷,故A错误.沿着电场线电势逐渐降低,由于不清楚电场的具体方向,所以不能判定电势的变化情况,选项B错误.电场线密的地方电场的强度大,电场线疏的地方电场的强度小,所以a受力减小,加速度减小,b受力增大,加速度增大,故C正确.物体做曲线运动,所受力的方向指向轨道的内侧,从图中轨道变化来看电场力都做正功,动能都增大,速度都增大,所以电势能都减小,故D错误.故选C.

单项选择题
阅读理解

阅读理解。

      It is possible to do many simple tricks with numbers. Here is one trick. It has seven steps.

      First, write down your house number. For example, if your address is 73 Lemon Street, you would write

down 73.

      Next, double it. In other words, multiply it by two. Then, add five to this doubled number. For example,

if your address was 73and you doubled it, you would get 146. Then, if you added five, you'd get 151. 

      So, to repeat the first three steps, write down your house number, double it, and add five.

      Fourth, multiply this number by 50. In our example here, if you multiply 151 by 50, you'll get 7550.

      The fifth step is to add your age to this total. For example, if you're 26 years old, you should add 26 to this

total. In our example here, the result would be 7550 plus 26, you'll get 7576.

      Sixth, you have to add the number of days in a year, which is 365. In our example here, 365 added to 7576

is 7941.

      The seventh and final step is this: subtract 615 from the number that you have. In our example, 7941

minus 615 is 7326.

      The result here, 7-3-2-6, is the trick. The first part of the number is the address and the last part of the

number is the age of the person. That is, 73 is the address that we started with, and 26 is the age that we

used.

      If you follow these seven steps with any address and the age of any person. You will get the same result.

1. According to the trick, what number can you get if you are 16 years old and your house number is 85? [ ]

A. 1685

B. 8516

C. 8165

D. 1658

2. What's the correct match for"multiply, plus, and minus"? [ ]

A. "×, +, and-"

B. "÷, -, and +"

C. "×, -, and+"

D. "÷, +, and-"

3. How can your age number appear at the last part of the result? [ ]

A. It's really a trick.

B. By taking all the steps except Step2 and Step 3.

C. By taking Step 6and Step 7.

D. By taking all the steps.

4. What's the secret of the trick? [ ]

A. It's impossible to know.

B. By taking Step 2 and Step 4, we get the formula(公式):your address number ×2×50.

C. By taking all the steps except 1 and 2, we get the formula: 5×50+your age number+365-615=your

     age number.

D. Both B and C.