8-48 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} \theta&=8.0\degree\\ S&=815\ut{m} \end{cases} $$ $$\Delta h = S\sin\theta$$ $$\Sigma \Delta E=0,$$ $$\Delta \KE+\Delta \GE=0$$ $$ \begin{aligned} \Delta \KE&=-\Delta \GE\\ \Delta \(\frac{1}{2}mv^2\)&=-\Delta(mgh)\\ \Delta \(v^2\)&=-2g\Delta h\\ {v_f}^2-{v_i}^2&=-2g(S\sin\theta)\\ \end{aligned} $$ $$ \begin{aligned} v_i&=\sqrt{2gS\sin\theta}\\ &=1630g\sin8\degree\\ &\approx 2224.659681563942\ut{m/s}\\ &\approx 2.2\times10^3\ut{m/s}\\ &\approx 2.2\ut{km/s}\\ \end{aligned} $$