问题 选择题

物体A.B用轻绳连接,A上端与一个轻弹簧相连,弹簧上端固定在铁架台上,如图所示。已知两物体的质量分别是mAmB, 开始时系统处于静止状态。现剪断连接A.B的细线,则B将自由下落,而A则在竖直方向做简谐运动。在B物体落到地面前的过程中,下面的说法中正确的是:

A.A.B组成的系统动量守恒

B.A物体的动量变化与B物体的动量变化大小相等、方向相反

C.弹簧弹力对物体A的冲量等于物体A的动量的增量

D.弹簧弹力对物体A的冲量等于重力对A.B的冲量之和再加上A.B的动量的增加量

答案

答案:D

A.B组成的系统受到重力、弹簧的弹力作用,不满足动量守恒的条件,A.B不对而选项D正确。对物体A来说,弹簧弹力与重力的冲量的矢量和等于它动量的增量。

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.

小题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.小题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小题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小题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.

多项选择题