8.
![](https://www.ebk.net.cn/tikuimages/8/2017/600/shoutiniao19/553c825f404ffed8360e4e9e3d08f1c6.png)
如图所示,均匀介质中两波源\(S_{1}\)、\(S_{2}\)分别位于\(x\)轴上\(x_{1}=0\)、\(x_{2}=14m\)处,质点\(P\)位于\(x\)轴上\(x_{P}=4m\)处,质点\(Q\)位于\(x_{Q}=9m\)处,\(t=0\)时刻,波源\(S_{1}\)由平衡位置开始向\(y\)轴正方向做简谐运动,波源\(S_{2}\)由平衡位置开始向\(y\)轴负方向做简谐运动,振动周期均为\(T=0.1s\),传播速度均为\(v=40m/s\),波源\(S_{1}\)的振幅为\(A_{1}=2cm\),波源\(S_{2}\)的振幅为\(A_{2}=3cm\),则\((\) \()\)