问题 问答题

体育课上进行爬杆活动,使用了一根质量忽略不计的长杆,长杆竖直固定在地面上,一个质量为40kg的同学(可视为质点)爬上杆的顶端后,自杆顶由静止开始匀加速紧接着又匀减速滑下,滑到杆底时的速度恰好为零.测得杆对地的最大压力为460N,最小压力为280N,人下滑的总时间为3s.求该同学下滑过程中的最大速度及杆长.

答案

设加速下滑时的加速度为a1,运动时间为t1

则有mg-280=ma1

υm=a1t1

减速下滑时的加速度大小为a2,运动时间为t2

则有460-mg=ma2

υm=a2t2=a2(3-t1

设杆长为l,则有l=

υm
2
×t

解得:υm=3m/s  

  l=4.5m

答:该同学下滑过程中的最大速度3m/s及杆长4.5m.

阅读理解

My problems started after I went to a boar ding school. I was only 14, and at first I missed my family a lot. I often called them and cried on the phone. But after two weeks, I found I enjoyed being with my classmates at school.

I had many friends who were boys. I thought of them as my best friends - but only friends. I never guessed my friendships with boys would become a problem.

Then, three months later, my friends told me that some teachers and girls said I was hanging out with boys all day long in order to get attention from them. Seven months after that, the head teacher Mr. Wang asked the class to choose some students to join the Student Union. I thought I could win for I was doing well in school. I'd already won prizes for the best math and English exams. A week later, the list came out and it didn't include me. I was sad.

Mr. Wang came to me and sai d, "Don't be sad. I know you're excellent! Maybe

you're a little distant from the girls in our class. They don't know much about you, so some of them didn't choose you. It doesn't matter. Do your best to get along well with everyone and I think you'll make it next time."

小题1:What was the writer's problem when she first entered the boarding school?

A.She didn't like her new school.

B.She didn't get along well with her classmates.

C.She missed her family very m uch.

D.She didn't like her new teacher.小题2:Many of the writer's friends in her new school were _______.

A.teachers

B.boys

C.girls

D.women小题3:Why did the writer fail to join the Student Union?

A.Her teachers didn't like her.

B.She was a poor student.

C.Some girls didn't choose her.

D.She likes showing off herself.小题4:Which of the following is NOT true, according to the passage?

A.The writer won prizes for the best science and English exams.

B.The writer didn't realize that her friendships with boys would cause problems.

C.The writer was sad because she failed to join the Student Union.

D.The teacher thought she was an excellent student

单项选择题