问题 选择题

M、N是某电场中一条电场线上的两点,若在M点释放一个初速度为零的电子,电子仅受电场力作用,并沿电场线由M点运动到N点,其电势能随位移变化的关系如图所示,则下列说法正确的是(  )

A.电子在N点动能小于在M点动能

B.N点电场强度小于M点电场程度

C.若作该电子运动的v-t图象则图象的斜率越来越大

D.电子运动的轨迹为曲线

答案

电子从M运动到N过程中,只受电场力,电场力做正功,电势能减小,动能增加,因此N点动能大于M点的,故A错误;

根据图象可知电子做加速度逐渐减小的加速运动,因此电场强度逐渐减小,B正确,v-t图象上斜率表示加速度,故v-t图象的斜率越来越小,故C错误;

带电粒子初速度为零且沿电场线运动,其轨迹一定为直线,故D错误.

故选B.

选择题
阅读理解

Many of us like cooking but never have much time for it. Helen Fry’s new book Quick Cooking has been specially written for busy people. It has over 1,000 recipes, from the famous Spanish gazpacho to Swedish smorgasbord. The book is well written and the photographs and drawings are clear. (They are like those in the excellent little Quick Dressmaking and Quick Gardening.) The book has a strong plastic cover. It is easy to find your way around it too. And busy people, notice this! Mrs. Fry tells you how much time you need in order to get each dish ready.

Quick Cooking has 4 parts, one for each season. This helps you to use fresh fruit and vegetables when they are cheaper—and, of course, better. There are a lot of exciting ideas from foreign countries, and most of the recipes are easy to follow. You take something simple like a chicken or some cheese, and make and unusual dish out of it. For example, there are no fewer than 40 recipes for eggs! Mrs. Fry does not plan complete meals for the “quick book”. The beginners will have to find out a lot of things for himself—or herself. But this ought not to be difficult with such a good book. I wanted to try many of the recipes as soon as I read them. For people with little spare time Helen Fry’s Quick Cooking is excellent value. 

1. Helen Fry’s book is called Quick Cooking because ___.

A. you can cook all the dishes in it quickly

B. there is over 1,000 recipes in it

C. it is written for people who don’t have much time

D. it tells you how to cook all kinds of food quickly

2. Busy people should notice that _____.

A. all the recipes in the book are easy to follow

B. there are clear photographs and drawings in the book

C. the book has a strong cover

D. they are told how long each dish takes to cook

3. This passage is most probably ____.

A. a book review             B. a notice

C. a letter to an editor         D. an introduction on cooking

4. We can infer from the passage that _____.

A. Helen Fry is good at writing books quickly

B. complete meals are planned only for beginners

C. there are quite a few “quick books” for busy people

D. beginners are advised to start making meals out of the cheapest materials