问题 选择题

小明同学在学习中勤于思考,并且善于动手,在学习了圆周运动知识后,他自制了一个玩具,如图所示,用长为r的细杆粘住一个质量为m的小球,使之绕另一端O在竖直平面内做圆周运动,小球运动到最高点时的速度v=

gr
2
,在这点时(  )

A.小球对细杆的拉力是

mg
2

B.小球对细杆的压力是

mg
2

C.小球对细杆的拉力是

3
2
mg

D.小球对细杆的压力是mg

答案

根据牛顿第二定律得:mg+F=m

v2
r
,代入解得:F=-
1
2
mg
,知细杆对小球表现为支持力,所以小球对细杆表现为压力,大小为
1
2
mg
.故B正确,A、C、D错误.

故选:B.

阅读理解

阅读下列新闻及相关信息,并按照要求匹配信息。

A.FIFA agrees on heavy punishments to stamp out racism

ZURICH: Soccer’s world governing body FIFA agreed on Thursday to punish acts of racism with heavy punishments including taking away points and disqualification from competitions.

B. England face uphill task in the third test

MUMBAI: England will fight against all the probabilities to prevent a second straight series defeat when they face India in the third and final test starting on Saturday.

C. Disease-free chickens hit the market

GUANGZHOU: The first group of 200,000 live, quality-assured chickens, which wear colored plastic rings around their feet, hit Guangzhou’s markets on Friday, at a time when the threat of bird flu has kept chickens off many menus.

D. Football bosses deny Schweinsteiger betting report

BERLIN: German football chiefs on Thursday made a strong statement of the wrong saying that a newspaper says that Bayern Munich star Bastian Schweinsteiger was the international footballer involved in a betting.

E.Zhangs to lead Chinese team at the world championships(锦标赛)

Figure skaters Zhang Dan and Zhang Hao, whose heroic silver was a high point of last month’s Turin Winter Olympics, are ready to make China into pairs more noticeable at the world championships next week in Calgary.

F.Ministry looks to prevent soil from ruin

The two square meters of land covered with black soil that were once the pride of farmer Lei Guangsheng are now a problem without an easy solution.

请阅读下面的信息,了解五位成员的兴趣。然后进行信息匹配。

小题1:Tony is very interested in agriculture, so he wants to know about something that is happening in the countryside.

小题2:Collins focuses his attention on people’s health, so he would like to know what has happened in this field.

小题3:Jesse likes sports very much. Next week the winter holidays will begin and he wants to see some great events happening in the following week.

小题4:Jack takes great interest in collecting sportsmen’s personal information, especially about their bad behavior.

小题5:Harry is a football fan. He often watches football games invented in old England. Now he needs to know some decision made by the organization.

单项选择题