a/ \(\omega^2=\frac{k}{m}\Rightarrow\omega=\sqrt{\frac{80}{0,8}}=10\left(rad/s\right)\)
\(\Rightarrow T=\frac{2\pi}{10}=\frac{\pi}{5}\left(s\right)\)
\(v_{max}=\omega A=10.5=50\left(cm/s\right)\)
b/ \(v=\frac{1}{2}v_{max}\Leftrightarrow v=25\left(cm/s\right)\)
\(W_t=W-W_d=\frac{1}{2}kA^2-\frac{1}{2}mv^2=\frac{1}{2}.80.0,05^2-\frac{1}{2}.0,8.0,25^2=0,075\left(J\right)\)