quãng đường \(S=12,5=\frac{5A}{2}=2A+\frac{A}{2}\Rightarrow\Delta\varphi=\pi+\varphi_{\frac{A}{2}}\)
tại t=0 \(\left\{{}\begin{matrix}x=5.cos\pi=-5\\v=0\end{matrix}\right.\) => đi dc \(\frac{A}{2}\) thì vật quét 1 góc \(\frac{\pi}{3}\)
\(\Rightarrow\Delta_{\varphi}=\pi+\frac{\pi}{3}=\frac{4\pi}{3}\Rightarrow\Delta_t=\frac{\Delta_{\varphi}}{\omega}=\frac{4\pi}{3}:10\pi=\frac{2}{15}s\)