`A)`

`x =A cos(\omega t + \varphi) => x = A cos(\varphi) = 10 . cos(\pi/3) = 10. 1/2 = 5 cm`

`=>` Đúng

`B)`

Li độ `x = -5\sqrt{3) cm -= -0,05\sqrt{3} m`

`=> v = \omega \sqrt{A^2 - x^2} => v = 4\pi . \sqrt{0,1^2 - (0,05\sqrt{3})^2} = 4\pi . \sqrt{0,01 - 0,0075} = 1\pi . \sqrt{0,0025 = 4\pi . 0,05} = 20\pi`  `cm`/`s`

`=>` Đúng

`C)`

`W = 1/2m\omega^2A^2 = 1/2 . 1. (4\pi)^2 . 0,1^2 = 1/2 . 16\pi^2 . 0,01 = 8\pi^2 . 0,01 = 0,08\pi^2`

`=> W = 0,08 . 10 = 0,8 J`

`=>` Sai

 `D)`

`W_đ = 1/2m\omega^2A^2 = W . sin^2(\omega t + \varphi)`

`=> f_(W_đ) = 2f = 4Hz`

`=>` Sai

  `\color{#1AD5F7}{⋆⟡D}\color{#1AD5F7}{r}\color{#4DA6E6}{a}\color{#668EDD}{g}\color{#8077D5}{o}\color{#995FCD}{n}\color{#EA2F90}{⟡⋆}`