问题 选择题

B如图所示,两个质量不同的物体A和B,分别从两个相同高度光滑斜面和光滑圆弧形斜坡的顶点,从静止开始下滑到底部,下列说法正确的是(  )

A.它们到达底部时的速度大小相等

B.下滑过程中重力做的功相等

C.它们在顶点时的机械能相等

D.它们到达底部时的动能相等

答案

A、根据WG=mgh得,质量不等,则重力不等,重力做功不相等.由mgh=

1
2
mv2-0得,到达底端动能等于重力做功的大小,所以到达底端的动能不等.v=
2gh
,与质量无关,所以到达底端的速度大小相等.故A正确,B、D错误.

C、在顶点时,由于质量不等,则重力势能不等,动能都为零,所以机械能不等.故C错误.

故选A.

阅读理解

阅读理解

     Where do most writers get their ideas? For Yoshiko Uchida, it all began with Brownie, a

five-month-old puppy. So excited was Yoshiko by Brownie’s arrival that she started keeping a

journal, writing about all the wonderful things Brownie did and the progress he made.

     Soon she was writing about other memorable events in her life, too, like the day her family got their

first refrigerator. She also began writing stories, thanks to one of her teachers. Yoshiko wrote stories

about animal characters such as Jimmy Chipmunk and Willie the Squirrel. She kept on writing, sharing

the kitchen table with her mother, who wrote poems on scraps of paper and the backs of envelopes.

     Yoshiko grew up in the 1930s in Berkeley, California. Her parents, both of whom had been born in

Japan, provided a loving and happy home for Yoshiko and her sister. They also provided a stream of

visitors to their home who later found their way into Yoshiko’s stories. One visitor who later appeared

in several of Yoshiko’s stories was the bad-tempered Mr. Toga, who lived above the church that her

family attended. Mr. Toga would scold anyone who displeased him. The children all feared him and

loved to tell stories about how mean he was and how his false teeth rattled (咯咯响) when he talked.

     Yoshiko also included in her stories some of the places she visited and the experiences she had.

One of her favorite places was a farm her parents took her to one summer. The owners of the farm,

showed Yoshiko and her sister how to pump water from the well and how to gather eggs in the

henhouse. They fed the mules that later pulled a wagon loaded with hay while Yoshiko and the others

rode in the back, staring up at the stars shining in the night sky. Yoshiko, who lived in the city, had

never seen such a sight. As Yoshiko gazed up at the stars, she was filled with hope and excitement

about her life. The images of that hayride stayed with her long after the summer visit ended, and she

used them in several of her stories.

     The experiences Yoshiko had and the parade of people who marched through her young life

became a part of the world she created in over twenty books for young people, such as

The Best Bad Thing and A Jar of Dreams. Because of such books, we can all share just a little bit

of the world and the times in which this great writer grew up.

1. The author tells about Mr. Toga’s false teeth in Paragraph 3 in order to ____________.

A. show health care was not good enough in Berkeley during the 1930s

B. provide an interesting detail in Yoshiko’s life and stories

C. show Yoshiko’s young life was difficult and frightening

D. tell about a beloved relative who helped Yoshiko learn how to write

2. In Paragraph 4 “the stars” probably refer to ____________.

A. family relationships

B. terrors in the night

C. limitless possibilities

D. sacrifices to benefit others

3. What does the underlined part in the last paragraph mean?

A. Yoshiko loved to write about parades.

B. Yoshiko met many interesting people.

C. Yoshiko liked to go for long walks with others.

D. Yoshiko preferred to talk to her pets instead of to people.

4. What is the main idea of this story?

A. People who live in the city should spend as much time as they can in the country.

B. Writers like Yoshiko Uchida must communicate with as many writers as possible.

C. Those who move to the United States often miss their homelands for many years.

D. Writers like Yoshiko Uchida look to the richness of their lives for writing sources.

单项选择题