Câu 1: 

a) Ta có: 

\(\begin{array}{l}
l = 4.\dfrac{\lambda }{2} = 2\lambda  \Rightarrow 175 = 2\lambda  \Rightarrow \lambda  = 87,5\left( {cm} \right)\\
f = \dfrac{v}{\lambda } = \dfrac{{100}}{{87,5}} = \dfrac{8}{7}\left( {Hz} \right)
\end{array}\)

b) Ta có: 

\(l = 3.\dfrac{\lambda }{2} = 1,5\lambda  \Rightarrow 175 = 1,5\lambda  \Rightarrow \lambda  = \dfrac{{350}}{3}\left( {cm} \right)\)

Câu 2: 

Ta có: 

\(\begin{array}{l}
{v_{\max }} = \omega A = 1\left( {cm/s} \right)\\
{a_{\max }} = {\omega ^2}A = 1,57\left( {cm/{s^2}} \right)\\
 \Rightarrow \omega  = 1,57\left( {rad/s} \right)\\
 \Rightarrow A = \dfrac{1}{{1,57}} = 0,64\left( {cm} \right)
\end{array}\)