题目

Hi, I’m Jane! I’m twelve years old. I have a brother. He’s ten. His name is John. We have different(不同的) hobbies. I like watching TV very much. I have a small TV in my room. I like watching baseball games on TV. I think they’re relaxing. And I like carrots and eggs, too. I think they are good for me.John likes playing computer games. He thinks they’re great fun, but I think they’re boring. John doesn’t like fruit. He likes French fries and ice cream. And he likes hamburgers, too. I don’t think they’re healthy. I don’t eat them.【1】Jane is John’s .A.friend B.sist有两列简谐横波a、b在同一媒质中沿x轴正方向传播，波速均为v=2.5m/s。在t=0时，两列波的波峰正好在x=2.5m处重合，如图所示。求：①两列波的周期分别为多少?②当t1=0.4s时，横波b的传播使质点P的位移为多少?③t=0时，两列波的波峰重合处所有位置。