问题 选择题

如图所示,在水平天花板的A点处固定一根轻杆a,杆与天花板保持垂直,杆的下端有一个轻滑轮O.另一根细线上端固定在该天花板的B点处,细线跨过滑轮O,下端系一个重量为G的物体.BO段细线与天花板的夹角为θ=30°,系统保持静止,不计一切摩擦.下列说法中正确的是(  )

A.细线BO对天花板的拉力大小是

B.a杆对滑轮的作用力大小是

C.a杆和细线对滑轮的合力大小是G

D.a杆对滑轮的作用力大小是G

答案

D

题目分析: 对重物受力分析,受到重力和拉力T,根据平衡条件,有T=G,同一根绳子拉力处处相等,故绳子对天花板的拉力也等于G,故A错误;对滑轮受力分析,受到绳子的压力(等于两边绳子拉力的合力,两绳子拉力大小相等),以及杆的弹力(向右上方的支持力),根据平衡条件,结合几何关系,有F=T=G,故B错误,D正确;由于滑轮处于平衡状态,故a杆和细线对滑轮的合力大小是零,故C错误;

阅读理解

     Here is a poster- on a middle school web site. Read the web-site poster.                      

     Going, Going, Gone!

    The Haynes Middle School Parent-teacher Organization

     nvites you to attend our latest fund (基金) -raiser

    The Fourth Annual (每年一次) Haynes School Auction(拍卖)

     Saturday, May 10

     6:00 p.m.--11:00 p.m. in the school hall

     6:00 p.m.--6:30 p.m.: All items for auction are previewed(预览).

     6:30 p.m.--7:00 p.m.: Silent auction begins.

     7:00p.m.--7:30p.m.: Highest bidders(出价人) from silent auction are determined.

     7:30--11:00 p.m.: Main auction begins.

     Items up for bid in the silent auction list in value from $ 5.00 to $ 30.00

     Items up for bid in the main auction include the following;

    1. Airline tickets to a place of your choice

    2. Weekend getaways at first-class hotels

    3. Season tickets to the Chicago Bears football game

    4. $ 50 gift tickets to local gift shops, restaurants, and salons

    5. Theater tickets to The Merchant of Venice

    Don't miss the boat! Book your tickets today.

     Last year, tickets sold out in five days!

     Tickets are sold on a first-come, first-served basis.

      $15.00 per person

     All the money from the auction will be given to the Haynes School computer lab.

1. Which of the following is not mentioned as being up for bid at the auction?

A. A movie pass to the local cinema.  

B. A weekend stay at a hotel.

C. A ticket to a restaurant.          

D. Airline tickets.

2. The more items that are given or bought for auction,             

A. the less money that will be charged for the tickets to the auction

B. the more money that can be raised to support the computer lab

C. the faster the ticket will be sold to the auction

D. the higher the value that will be placed on the items in the silent auction

3. The phrase" first-come, first-served" tells you that          

A. people can buy the tickets on the first day onl

B. the person who is first to arrive will receive a ticket at no charge

C. food and drinks will be served at the auction

D. tickets are sold in the order of who arrives first to buy them

4. Which of the following is most likely to happen at the year's auction?

A. The airline tickets will receive higher bids than any other item.

B. All items up of bid will be sold for at least twice their value.

C. More money will be raised this year than in any other year before.

D. Tickets for the event will be sold out in less than one week.

5. When dose the main auction begin?

A. 7.00p.m.--7.30p.m.              

B. 6.30p.m.--7.00p.m.

C.7.30p.m.--11.00p.m.          

D. 6.00p.m.--6.30p.m.

单项选择题 B1型题