3. The position of a rock (mass 2.5 kg) is given by $\vec{r}=0.020t^{3}\hat{x}+2.2t\hat{y}-0.060t^{2}\hat{z}$ in meter. Find the torque about z-axis at $t=2.0 s$?
(A) $-0.66\hat{x}+0.048\hat{y}-2.64\hat{z} N\cdot m$
(B) $-0.66\hat{x}+0.048\hat{y} N\cdot m$
(C) $0.144\hat{z} N\cdot m$
(D) $-2.64\hat{z} N\cdot m$
(E) None
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統計: 尚無統計資料
統計: 尚無統計資料