问题 问答题

如图位于竖直平面上半径为R的1/4圆弧光滑轨道AB,A点距离地面高度为H,质量为m的小球从A点由静止释放,通过B点对轨道的压力为3mg,最后落在地面C处,不计空气阻力,求:

(1)小球通过B点的速度

(2)小球落地点C与B点的水平距离x.

答案

(1)在B点对小球由牛顿第二定律得:N-mg=m

v2
R
…①

由牛顿第三定律得:N=N′=3mg…②

解得:v=

2gR

(2)小球从B至C做平抛运动:

水平方向:x=vt…③

竖直方向:H-R=

1
2
gt2…④

解得:x=2

R(H-R)

答:(1)小球通过B点的速度为

2gR

(2)小球落地点C与B点的水平距离x为2

R(H-R)

写作题

阅读下面的短文,然后按照要求写一篇150词左右的英语短文。

If you like to break things when you are unhappy, the Nanjing Zhonghua Middle School is the school for you. This term, Nanjing Honghua Midlde School will build a "stress wall" to help students who feel unhappy because of schoolwork or for other reasons.

Tao Dehua, a leader at the school said the idea of a stress wall started when footprints were found on some newly painted walls and some school windows were broken.

"These things happen because some students feel lots of pressure from their studies or because they don't get along well with other students. When under stress, the body get ready to either run or fight and becomes very nervous. Hitting the wall can help relax the body and take away stress," Tao said.

"Tests and homework make me Sad," said Lu Yan, a junior girl."I can't wait to hit the wall. It will help me a lot with my problems."     

Another girl student who wouldn't give her name said that the wall won't help."Mainly because it can't talk," she said. "I need to talk to someone when I'm sad."

【写作内容】

1、以约30个词概括这段短文内容;

2、然后以约120个词就“Should the stress wall be built"这个主题发表你的看法,并

包括以下要点:

(1)学生的压力来源;

(2)是否该建此墙;

(3)提供一些其他有效的减压方法。

【写作要求】

l、可以参照阅读材料但不得直接引用原文的句子;

2、作文中不得出现真实的姓名和学校名称。

【评分标准】

概括准确,语言规范,内容合适,篇章连贯。

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