2-46 할리데이 10판 솔루션 일반물리학

$$\begin{cases} x_0 = 1800\ut{m}\\ x_1 = 0\\ v_0 = 0\\ a = -g = -9.80665\ut{m/s^2}\\ \end{cases}$$
(a)$\abs{v_1}=?$ $$2a\Delta x = v^2-v_0^2,$$ $$v^2 = 2a\Delta x +v_0^2$$ $$\begin{aligned} \abs{v_1} &= \sqrt{2(-g)(-x_0) +0^2}\\ &= \sqrt{2gx_0}\\ &= \sqrt{2(9.80665\ut{m/s^2})(1800\ut{m})}\\ &= \sqrt{\frac{1765197}{50}}\ut{m/s}\\ &\approx 187.8934272400182\ut{m/s}\\ &\approx 187.9\ut{m/s} \end{aligned}$$
(b) $$\begin{aligned} &\sqrt{\frac{1765197}{50}}\ut{m/s}\cdot\frac{3600\ut{s}}{1\ut{h}}\cdot\frac{1\ut{km}}{1000\ut{m}}\\ =&\frac{27 \sqrt{392266}}{25}\ut{km/h}\\ =&676.4163380640654\ut{km/h}\\ \end{aligned}$$ $$ \title{Not Safe}$$