Câu hỏi 38

Ta có: 

\(\left\{ \matrix{
\omega = 8\pi (rad/s) \hfill \cr
0,04\pi x = {{2\pi x} \over \lambda } \hfill \cr} \right. \Rightarrow \left\{ \matrix{
T = 0,25s \hfill \cr
\lambda = 50cm \hfill \cr} \right. \Rightarrow v = {\lambda \over T} = 200cm/s\)