问题 选择题

某质点做曲线运动时:(   )

A.在某一点的速度方向是该点曲线的切线方向

B.在任意时间内,位移的大小总是大于路程

C.在某段时间里质点受到的合外力可能为零

D.速度的方向与合外力的方向必不在同一直线上

答案

AD

题目分析:曲线运动的速度方向与过该点的曲线的切线方向相同,所以A正确.位移是指从初位置到末位置的有向线段,它是直线的距离,而路程是经过的轨迹的长度,在曲线运动中,位移的大小要小于路程的大小,所以B错误.做曲线运动的质点,如果合外力为零,那它就要做匀速直线运动,不是曲线运动了,所以C错误.物体做曲线运动的条件是合力与速度不在同一条直线上,既然是曲线运动,那么速度的方向与合外力的方向一定不在一直线上,所以D正确.

故选AD

点评:物体做曲线运动的条件是合力与速度不在同一条直线上,速度的方向与该点曲线的切线方向相同,位移是指从初位置到末位置的有向线段,而路程是经过的轨迹的长度.

阅读理解

阅读理解。

     Remembering names is an important social skill. Here are some ways to master it.

     Recite and repeat in conversation.

     When you hear a person's name, repeat it. Immediately say it to yourself several times without moving

your lips. You could also repeat the name in a way that does not sound forced or artificial.

     Ask the other person to recite and repeat.

     You can let other people help you remember their names. After you've been introduced to someone,

ask that person to spell the name mad pronounce it correctly for you. Most people will be pleased by the

effort you're making to learn their names.

     Admit you don't know.

     Admitting that you can't remember someone's name can actually make people relaxed. Most of them

will feel sympathy if you say. "I'm working to remember names better. Yours is right on the tip of my

tongue. What is it again?"

     Use associations.

     Link each person yon meet with one thing you find interesting or unusual. For example, you could make

a mental note:"Vicki Cheng-tall, black hair." To reinforce you're your associations, write them on a small

card as soon as possible.

     Limit the number of new names you learn at one time.

     When meeting a group of people, concentrate on remembering just two or three names. Free yourself

from remembering every one. Few of the people in mass introductions expect you to remember their names.

Another way is to limit yourself to learning just first names. Last names can come later.

     Go early.

     Consider going early to conferences, parties and classes. Sometimes just a few people show up on time.

That's fewer names for you to remember. And as more people arrive, you can hear them being introduced

to others-an automatic review for you.

1. How will most people feel when you try hard to remember their names?

A. They will be moved.

B. They will be annoyed.

C. They will be delighted.

D. They will be discouraged.

2. If you can't remember someone's name, you may _____.

A. tell him the truth

B. tell him a white lie

C. ask him for pity

D. ask others to help you

3. When you meet a group of people, it is better to remember _____.

A. all their names

B. a couple of names first

C. just their last names

D. as many names as possible

4. What does the text mainly tell us?

A. Tips on an important social skill.

B. Importance of attending parties.

C. How to make use of associations.

D. How to recite and repeat names.

填空题