6-7 할리데이 11판 솔루션 일반물리학

$$\ab{a}$$ $$\Sigma \vec F = 0 \Harr \Delta \vec v=0,$$ $$ \begin{cases} \Sigma F_x &= 0\\ \Sigma F_y &= 0\\ \end{cases} $$ $$ \begin{cases} mg\sin\theta-\mu F_N&=0\\ F_N-mg\cos\theta&=0 \end{cases} $$ $$ \begin{aligned} mg\sin\theta-\mu mg\cos\theta&=0\\ \end{aligned} $$ $$\therefore \mu =\tan\theta$$ $$ \begin{cases} -mg\sin\theta-\mu F_N &= m a_x\\ F_N-mg\cos\theta&=0 \end{cases} $$ $$\therefore a=-2g\sin\theta$$ $$2aS=v^2-{v_0}^2,$$ $$ \begin{aligned} S&=\frac{v^2-{v_0}^2}{2a}\\ &=\frac{-{v_0}^2}{2(-2g\sin\theta)}\\ &=\frac{{v_0}^2}{4g\sin\theta}\\ \end{aligned} $$ $$\ab{b}$$ $$\text{NO}$$ $$\because \Sigma \vec F = 0 \Harr \Delta \vec v=0$$