\(1)\)

*\(T=\dfrac{2\pi}{\omega}=\dfrac{2\pi}{\pi}=2(s)\)

* L=2A=2.4=8(cm)

* Ở vị trí cân bằng, v đạt giá trị lớn nhất \(|v|_{max}=A\omega=4\pi(cm/s)\)

*\( t=0, \quad \varphi=\dfrac{\pi}{4}\Rightarrow\) Vật chuyển động theo chiều âm.

\(\longrightarrow C.\)

\(2)\\T=\dfrac{\Delta t}{N}=\dfrac{10}{5}=2(s)\\\Rightarrow \omega=\dfrac{2\pi}{T}=\dfrac{2\pi}{2}=\pi(rad)\\\Rightarrow v_{max}=A\omega =4\pi(cm/s)\\3)\\a=0,2\pi^2 (m/s^2)=20\pi^2(cm/s^2)\\\begin{cases} a_{max}=A\omega^2=0,2\pi^2(m/s^2)\\v_{max}=A\omega=10\pi (cm/s)\end{cases}\Rightarrow \dfrac{a_{max}}{v_{max}}=\dfrac{A\omega^2}{A\omega}=\omega=\dfrac{20\pi^2}{10\pi}=2\pi(rad)\\\Rightarrow T=\dfrac{2\pi}{\omega}=\dfrac{2\pi}{2\pi}=1(s)\\v_{max}=A\omega=10\pi(cm/s)\Rightarrow A=\dfrac{10\pi}{\omega}=\dfrac{10\pi}{2\pi}=5(cm)\\\longrightarrow A.\)