机械横波某时刻的波形图如图所示，波沿x轴正方向传播，质点P的横坐标x＝0.32m．从此时刻开始计时．
(1)若经过时间0.4s再一次出现相同波形图，求波速．
(2)若P点经0.4s第一次达到正向最大位移，求波速．
(1)2m/s (2)0.3m/s
(1)依题意，周期T＝0.4s，波速
(2)波沿x轴正方向传播，
P点经0.4s恰好第一次达到正向最大位移，波速
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| The night started out ordinarily enough. Jack and Tara, our 1 , were in their small beds surrounded by toy animals. My husband, Pat, and I went to sleep 2 . 3 after midnight, Jack quietly touched me. "Mommy, I want to stay with you. I promise I won't take much room." I shifted 4 to make room. My son soon fell asleep. An hour later, Tara cried and I carefully went downstairs. "Mommy, my 5 is an stuffed up (堵住). I can't really breathe very well. Will you please 6 with me a little while?" Tara doesn't often get up at night. 7 . I decided to be there for her. She soon fell asleep. I returned to my own bed. I was determined to sleep. But to my 8 , I found Jack sleeping on my side of the bed. He looked so 9 that I couldn't remove him. Quietly and carefully, I lay down between 10 and Jack. I did manage to get some sleep 11 I heard Tara's voice again. I returned to 12 Tara. "Mom, please lie down with me a little bit. I had a bad dream, and I'm so 13 ." "Of course, honey. It was only a dream Mommy's here and 14 is okay." We fell asleep 15 each other's arms. Even in my sleepy state, I thought of 16 these nights of merry-go-round (一连串的繁忙活动) beds will be over. In their place, my twins will be grown 17 before I'm ready, our children' rooms will be much too 18 and empty. So it is especially on days when I'm worn out after a night on this mom's merry-go-round that I remind 19 that these very days and nights are, in fact, "the good old days", ever so 20 . | ||||
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