问题 多选题

如图所示,长为l的轻杆,一端固定一个小球,另一端固定在光滑的水平轴上,使小球在竖直平面内作圆周运动,关于小球在过最高点时的速度v,下列叙述正确的是(  )

A.v的最小值为

gl

B.v由零逐渐增大,向心力也逐渐增大

C.v由

gl
值逐渐增大,杆对小球的弹力也逐渐增大

D.v由

gl值逐渐减小,杆对小球的弹力也逐渐减小

答案

A、细杆拉着小球在竖直平面内做圆周运动,在最高点的最小速度为零.故A错误.

B、根据F=m

v2
R
知,速度增大,向心力增大.故B正确.

C、当v=

gl
时,杆子的作用力为零,当v>
gl
时,杆子表现为拉力,速度增大,拉力增大.故C正确.

D、当v<

gl
时,杆子表现为支持力,速度减小,支持力增大.故D错误.

故选BC.

阅读理解

Body language is quiet, secret and most powerful language of all. It speaks louder than words.

According to specialists, our bodies send out more messages than we realize. In fact, non-verbal(非语言) communication takes up about fifty percent of what we usually mean. And body language is especially important, when we try to communicate across cultures.

Indeed, what is called body language is so much a part of us that it’s actually often unnoticed. And misunderstandings happen as a result of it. For example, different cultures treat the distance between people differently. Northern Europeans usually do not like having bodily contact(接触),even with friends. And certainly not with strangers. People from the Latin American countries, on the other hand, touch each other quite a lot. So it’s possible that in conversation it may look like a Latino is following a Norwegian (挪威人)all over the room. The Latino, trying to express friendship, will keep moving closer. The Norwegian, very probably seeing this as rude behavior, will keep backing away, which the Latino will in return regarded as coldness.

Obviously, a great deal is going on when people talk. And only a part of it is in the words themselves. And when parties are from different cultures, there’s a strong possibility of misunderstanding. But whatever the situation is, the best advice is to obey the golden rule: Treat others as you would like to be treated.

小题1:You may find the passage in _____.

A, a science magazine  B. a guide book 

C. a sports newspaper  D. a story book

小题2:The underlined word this in paragraph 3 refers to ___.

A.the Norwegian keeps moving closer

B.the Latino follows the Norwegian

C.the Norwegian keeps backing away

D.the Latino’s way of expressing friendship小题3:Misunderstanding of body languages always happens because of the ___.

A.languages

B.friends

C.cultures

D.countries小题4:Which of the following is true?

A.people around the world have the same body languages

B.body language takes up about 50% of our communication

C.body language is the most important in our communication

D.body language is important when trying to communicate across cultures小题5:If a foreign friend gives a hug to you, you should___.

A.shake hands with him

B.give him a hug

C.refuse him

D.kiss him

多项选择题