2-49 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} H&=45.0\ut{m}\\ t&=2.00\ut{s}\\ h_1&=11.8\ut{m}\\ g&=9.80665\ut{m/s^2} \end{cases} $$ $$ S=vt-\frac{1}{2}at^2, $$ $$ \begin{aligned} h_1-H&=v(2)-\frac{1}{2}(-g)(2)^2\\ (11.8)-(45)&=v(2)-\frac{1}{2}(-g)(2)^2\\ \end{aligned} $$ $$ \begin{aligned} \abs{v}&=\abs{-\(\frac{83}{5}+g\)}\\ &=\frac{528133}{20000}\ut{m/s}\\ &=26.40665\ut{m/s}\\ &\approx 26.4\ut{m/s}\\ \end{aligned} $$