题目

位于坐标原点处的波源A沿y轴做简谐运动，A刚好完成一次全振动时，在介质中形成简谐横波的波形图如图所示，已知波速为2m/s，波源A简谐运动的周期为0.4s，B是沿波传播方向上的一个质点，则以下选项正确的是（______）A.图中x轴上AB之间的距离为0.4mB.波源A开始振动时运动方向沿y轴正方向C.此后的1/4周期内回复力对波源A一直做负功D.经半个周期质点B将向右迁移半个波长E.图示时刻质点C所受的合外力方向沿y轴正方向26、In the world today, all of the people need recreation (消遣). We cannot work all the time if we are going to keep healthy and enjoy life.     Everyone has his own way of relaxing. Perhaps the most popular form (形式) is to take part in sports. There are team sports, such as basketball and football. There are also individual (个人的) sports, such as swimming and running. Skating and mountain climbing are the most popular recreation for people who like to be outdoor. Not everyone who enjoys sports likes to take part in them. Many people like watching them on TV or listening to them on the radio. So many people like some forms of indoor recreation, such as watching TV, singing and dancing.     It doesn’t matter whether we like indoor recreation or take part in outdoor sports. It is important for everyone to relax from time to time, and enjoy some forms of recreation. (    ) 1. Which is the most popular form of recreation?         .         A．Sports     B．Watching TV   C．Sleeping   D．Singing and dancing (    ) 2. People want to take part in sports in order to         .         A．keep healthy and enjoy life   B．make friends C．find a good job                  D．make more money (    ) 3. Outdoor sports include(包括)           .         A．watching TV                     B．singing and dancing C．listening to the radio              D．skating and mountain climbing (    ) 4. Why do many people like watching sports on TV or listening to them on the radio?         A．Because they like sports, but they don’t like to take part in them. B．Because they don’t enjoy sports. C．Because they don’t enjoy life.         D．Because they don’t need recreation. (    ) 5. The passage mainly tells us that         .         A．basketball is a kind of team sport         B．everyone who enjoys sports should take part in them         C．different people have different ways of relaxing         D．indoor recreation is not as important as outdoor sports