埋弧自动焊时,焊缝两端的工艺板作用是防止缺陷产生。
参考答案:对
如图所示为一列沿x轴的负方向传播的简谐横波的图像,此时波刚好传播到x=1cm处,从此时开始计时,即t=0,已知t=0.7s时P点刚好第二次到达波峰,则( )
A.在t1=1.1s时,Q点第一次出现波峰
B.在t2=0.9s时,Q点第一次出现波峰
C.质点A和B在t=0时刻的位移是相同的
D.质点Q位于波谷时,质点P位于平衡位置
根据句意和首字母提示补全单词。
1. Lisa thinks tigers are ugly and penguins are b_________.
2. The old man is very f_________ to us.
3. Jean dislikes answering questions in class, because she is too s_________.
4. There are o_________ ways to go to the zoo.
5. His brother isn't tall. He is k_________ of short.