题目

一光滑圆环固定在竖直平面内，环上套着两个小球A和B（中央有孔），A、B间由细绳连接着，它们处于如图中所示位置时恰好都能保持静止状态。此情况下，B球与环中心O处于同一水平面上，AB间的细绳呈伸直状态，与水平线成300夹角。已知B球的质量为m，求：1.细绳对B球的拉力和A球的质量；2.若剪断细绳瞬间A球的加速度；3.剪断细绳后，B球第一次过圆环最低点时对圆环的压力. Finding a good friend can be quite difficult in the contemporary lives of teenagers. I was once baffled by what the definition of a good friend was, until I discovered a single step that, if taken, would make you the greatest friend.It is willingness. That is all it takes in order to be considered a good friends. Willingness must come from within your heart. Listening to your friends makes them feel important, special and wanted. The will to sacrifice for your friends will also take you a step closer to being a good friend. For instance, as you are about to leave to enjoy your Saturday night, your best friend calls you right when you are stepping out and tells you how terrible he feels, you must be willing to give up your Saturday night and go to your friends house and try to comfort him in anyway that you can.You must always be willing to give advice to your friends. For example, if your friends are in a situation where they do not know what to do, you must be willing to think things through and try to give them the best advice. The willingness to care is also a big must in being a good friend. You must care about how your friends feel and what they’re experiencing. Caring about your friends is one of the best things you can do, because when your friends are in their time of need and the whole world seems to turn against them, you must be the one to care about them.Nobody ever said being a good friend was easy. If you want to be a good friend, you have to be willing to listen, sacrifice, give advice and care about your friends.1.From this passage, we can learn that if a friends is confused about what to do next, we’d better_____ .A. give up our benefit to help himB. leave him alone and let him calm downC. listen to him quietlyD. offer him some reasonable advice2.The underlined word “baffled” in the first paragraph probably means “     ”.A. confused B. frustratedC. curious D. frightened3.We can learn from the passage that       .A. being a good friend is so difficult that few people can do itB. willingness can make a person a good friendC. friendship always means sacrificing your own interestsD. a person doesn’t need to care about his friends all the time4.What method does the author use to explain his opinion in the second paragraph?A. Making a definition. B. Citing an example.C. Making comparison. D. Listing some numbers.