2-19 할리데이 11판 솔루션 일반물리학

$$\begin{cases} d&=20.0\ut{m}\\ v_p&=14.0\ut{m/s}\\ D_{23}&=200\ut{m}\\ D_{12}&=300\ut{m} \end{cases}$$ $$\ab{a}$$ $$\begin{aligned} \Delta t &= \frac{d}{v}\\ &=\frac{20.0\ut{m}}{14.0\ut{m/s}}\\ &=\frac{10}{7}\ut{s}\\ &\approx1.428571428571429\ut{s}\\ &\approx1.43\ut{s} \end{aligned}$$ $$\ab{b}$$ $$\begin{cases} t_r&=0.500\ut{s}\\ a&=5.00\ut{m/s^2}\\ v_0&=0\\ t_\Ans &=t_r+\Delta t\\ S&=D_{12}-d=280\ut{m} \end{cases}$$ $$\begin{aligned} S&=v_0t+\frac{1}{2}at^2,\\ 280&=(0)\Delta t+\frac{1}{2}(5.00)(\Delta t)^2\\ \end{aligned}$$ $$\Delta t =4\sqrt{7}\ut{s}$$ $$\begin{aligned} t_\Ans &=0.500\ut{s}+4\sqrt{7}\ut{s}\\ &=\(\frac{1}{2}+4\sqrt{7}\)\ut{s}\\ &\approx 11.08300524425836\ut{s}\\ &\approx 11.1\ut{s}\\ \end{aligned}$$