4-46 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} H&=25\ut{m}\\ v_1&=4.00v_0\\ g&=9.80665\ut{m/s^2}\\ \end{cases} $$ $$ \begin{aligned} v_0&=v_x, \end{aligned} $$ $$ \begin{aligned} 2aS&=v^2-{v_0}^2,\\ 2(-g)(-25)&={v_{y1}}^2-{0}^2\\ 50g&={v_{y1}}^2\\ \end{aligned} $$ $$ \begin{aligned} {v_1}^2&={v_x}^2+{v_{y1}}^2\\ (4v_0)^2&={v_0}^2+50g\\ \end{aligned} $$ $$ \begin{aligned} v_0&=\sqrt{\frac{10g}{3}}\\ &\approx 5.717414917017422\ut{m/s}\\ &\approx 5.72\ut{m/s}\\ \end{aligned} $$