Đáp án:
a) \(\dfrac{A}{2}\) ; \( - \omega A\dfrac{{\sqrt 3 }}{2}\)
b) \( - \dfrac{{A\sqrt 3 }}{2}\) ; \(\dfrac{{\omega A}}{2}\)
c) \( - A\) ; \(0\)
d) \(0\) ; \( - \omega A\)
Giải thích các bước giải:
a) Ta có:
\(\begin{array}{l}
x = A\cos \left( {\omega t + \varphi } \right) = A\cos \dfrac{\pi }{3} = \dfrac{A}{2}\\
v = - \omega A\sin \left( {\omega t + \varphi } \right) = - \omega A\sin \dfrac{\pi }{3} = - \omega A\dfrac{{\sqrt 3 }}{2}
\end{array}\)
b) Ta có:
\(\begin{array}{l}
x = A\cos \left( {\omega t + \varphi } \right) = A\cos \left( { - \dfrac{{5\pi }}{6}} \right) = - \dfrac{{A\sqrt 3 }}{2}\\
v = - \omega A\sin \left( {\omega t + \varphi } \right) = - \omega A\sin \left( { - \dfrac{{5\pi }}{6}} \right) = \dfrac{{\omega A}}{2}
\end{array}\)
c) Ta có:
\(\begin{array}{l}
x = A\cos \left( {\omega t + \varphi } \right) = A\cos \left( \pi \right) = - A\\
v = - \omega A\sin \left( {\omega t + \varphi } \right) = - \omega A\sin \left( \pi \right) = 0
\end{array}\)
d) Ta có:
\(\begin{array}{l}
x = A\cos \left( {\omega t + \varphi } \right) = A\cos \left( {\dfrac{\pi }{2}} \right) = 0\\
v = - \omega A\sin \left( {\omega t + \varphi } \right) = - \omega A\sin \left( {\dfrac{\pi }{2}} \right) = - \omega A
\end{array}\)
