\(a)\\T=\dfrac{2\pi}{\omega}=\dfrac{2\pi}{2\pi}=1(s)\\f=\dfrac{1}{T}=1(Hz)\\\omega=2\pi(rad/s)\\\Rightarrow \begin{cases} T'=\dfrac{T}{2}=\dfrac{1}{2}(s)\\f'=2f=2(Hz)\\\omega'=2\omega=4\pi(rad/s)\end{cases}\\b)\\m=200g=0,2(kg)\\A=5(cm)=0,05(m)\)
Tại 2 biên, vật đạng thế năng cực đại
\(W_{t_{max}}=\dfrac{1}{2}m\omega^2A^2=\dfrac{1}{2}.0,2.(2\pi)^2.(0,05)^2\approx 0,01(J)\\c)\\t=\dfrac{1}{3}=\dfrac{T}{3}\\\Rightarrow x=-\dfrac{A}{2}=-\dfrac{5}{2}(cm)=-0,025(m)\\\Rightarrow W_t=\dfrac{1}{2}m\omega^2A^2=\dfrac{1}{2}.0,2.(2\pi)^2.(0,025)^2\approx 2,5.10^{-3}(J)\)
