问题 多项选择题

如图所示,在倾角为a的斜面上,放一质量为m的小球,小球和斜面及挡板间均无摩擦,当挡板绕O点逆时针缓慢地转向水平位置的过程中,则有()

A.斜面对球的支持力逐渐减小

B.斜面对球的支持力先减小后增大

C.挡板对小球的弹力先减小后增大

D.挡板对小球的弹力先增大后减小

答案

参考答案:A, C

解析:

对小球做受力分析,并将力平移为矢量三角形,如图

通过矢量三角形变化可知,斜面支持力不断变小,竖直挡板支持力先变小后变大,因此AC正确。

阅读理解

根据短文内容判断句子正误,正确的在题前括号内写“T”,错误的写“F”。

Dear Tom,

      I am studying in Beijing now. I have a day off today. Now let me tell you something about Beijing. In our

country people drive cars on the left side of the road, but here in Beijing, on the right side. Many people of

London go to work by car, while most people of Beijing go to work by bike. The weather of Beijing is better

than ours. It's fine for long here, but we have so many cloudy days in London. Students here work hard at

their lessons and a lot of people can speak English. It's a pity that students in our country don't work hard

and few people know Chinese. That's all for today. Please write to me soon.

                                                                                                                                 Your ever,

                                                                                                                                    Peter

( )1. This letter is from an English boy to his friend Tom.               

( )2. Peter is a farmer, not a student.                                   

( )3. Tom may be a middle school student in London.                       

( )4. In England cars go along the road on the right side.                

( )5. Peter thinks the Chinese students work harder than English students.

单项选择题