问题 单项选择题

截面直径为d的等直径圆杆,在外力偶矩作用下发生纯弯曲变形,若己知变形后中性层的曲率半径为户,材料的弹性模量为正,则该梁两端所承受的外力偶矩M的大小应为()。

A.A

B.B

C.C

D.D

答案

参考答案:A

解析:

梁发生纯弯曲时截面弯矩与外力偶矩M相等,圆截面绕中性轴的惯性矩I=又由曲率与弯矩间的物理关系

[点评] 本题主要考察横力弯曲时梁挠曲线的曲率与弯矩间的物理关系以及圆截面绕中性轴的惯性矩的计算。

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To Friend or Not to Friend

We all love our parents and turn to them when we're in need, but would you like them to hear the conversations you have with your friends on the school playground or lunch queue? Social networking sites have become extensions of the school hallways, so would you add your parents as “friends” and allow them to view your online activities and conversations with friends?

In the past the generation gap included a technology gap, where children were up to date with latest technology and parents were left behind, content to continue their day to day lives as they always had because they had no need to know more about technology. However, more and more parents are beginning to realize just how important social networks are in their lives. This realization has given many parents the motivation to educate themselves about social networking sites.

These days many people are attracted to social networking sites because they can choose who they have around them; there's also a certain amount of control over privacy that we don't get in real life. Sometimes we feel that privacy is violated when we must accept a “friend” request from a parent or family member.

It's a difficult choice whether or not to allow a parent to become a part of our online lives. On the one hand we don't want to “reject” their request because that might hurt their feelings or make them feel you have something to hide. On the other hand if you do accept, then you could have a sense of being watched and no longer feel free to comment or communicate the way you did before.

A recent survey suggested that parents shouldn't take it personally if their child ignores their request: “When a teen ignores a parent's friend request, it doesn't necessarily mean that they are hiding something, but it could mean that this is one part of their life where they want to be independent.”

Perhaps talking with parents and giving explanations would help soften the blow if you do choose not to add them to your friends list.

小题1:From Paragraph 2, we learn that ________.

A.parents feel secure about their privacy online

B.social networks successfully fill the generation gap

C.parents have realized the importance of social networks

D.social networks offer a platform for parents to communicate小题2:Teenagers may refuse a parent's friend request because ________.

A.they hide something from their parents

B.they are unwilling to be watched by parents

C.their parents tend to fall behind in technology

D.their parents make negative comments on them小题3:The passage is mainly about ________.

A.privacy online

B.social networks

C.the generation gap

D.parents' friend requests小题4:The passage is written mainly for ________.

A.parents

B.teenagers

C.teachers

D.researchers

填空题