4-62 할리데이 11판 솔루션 일반물리학

$$\begin{cases} \Delta x &= 45\ut{m}\\ \Delta y &= 2.9\ut{cm}\\ g&= 9.80665\ut{m/s^2}\\ \end{cases}$$ $$\ab{a}$$ $$\begin{aligned} S&=v_0t+\frac{1}{2}at^2,\\ -\Delta y &= v_{y0}t+\frac{1}{2}(-g)t^2\\ &= (0)t-\frac{1}{2}gt^2\\ \end{aligned}$$ $$\begin{aligned} t&= \sqrt{\frac{2\Delta y}{g}}\\ &\approx 0.07690483752841551\ut{s}\\ &\approx 0.077\ut{s}\\ &\approx 77\ut{ms}\\ \end{aligned}$$ $$\ab{b}$$ $$\begin{aligned} v_x &= \frac{\Delta x}{t}\\ &=\Delta x\sqrt{\frac{g}{2\Delta y}}\\ &\approx 585.1387434941656\ut{m/s}\\ &\approx 5.9\times10^2\ut{m/s}\\ \end{aligned}$$