问题 选择题

如图所示,一个用细绳系着的橡皮塞在水平面内做匀速圆周运动,此橡皮塞

A.只受重力

B.只受绳的拉力

C.受重力和绳的拉力

D.受重力、绳的拉力和向心力

答案

答案:C

题目分析:橡皮塞受到重力,绳子的拉力,其中绳子的拉力充当向心力,

故选C

点评:关键是知道向心力按性质分类的力,而是一个或者几个力的合力,为效果力

阅读理解

I can’t remember the date when I started collecting litter. But it was when I got tired of seeing litter near my home and realized that nobody else was going to pick it up.

I live close to a forest in Ohio, America. I can walk there within three minutes! I used to love going there to play with my dog. But one day there was so much litter there that I became very unhappy. I decided to clean up the forest.

I made my first trip to clean the forest one afternoon. I took a big black rubbish bag with me. Ten minutes later, my bag was full of cans, bottles, broken glass and newspapers.

Since that first trip three years ago, I’ve been to the forest four times a year to pick up litter. I’m often there for three hours. It makes me feel great to do something for the environment.

After each trip, I look at all the litter I’ve found. If any of it is recyclable(可回收的),I’ll keep it. I can’t understand why people drop litter. But I will keep picking it up until they stop dropping it.

I know I can only do a small bit to help the earth, but I still think it is important.

小题1:When did the writer begin to collect litter?

A. When he was very young.

B. After his home moved to a new place.

C. When he got tired of seeing litter near his home.

小题2:Where does the writer live?

A. He lives in a forest.

B. He lives in a place with much litter.

C. He lives near a forest.

小题3:The writer collects litter________.

A. in order to make the place clean

B. in order to make fun

C. in order to make money

小题4:Where does the writer collect litter?

A. In the forest      B. In the street         C.  In the park.

小题5:From the passage we infer(推断) __________

A.the writer always collects a lot of litter

B .the environment will be more beautiful if everyone tries to protect it.

C. the writer will go on collecting litter.

单项选择题