2-66 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} H&=40\ut{m}\\ \Delta x &=14\ut{m}\\ g&=9.80665\ut{m/s^2} \end{cases} $$ $$ \begin{aligned} S&=v_0t+\frac{1}{2}at^2,\\ -H&=(0)t+\frac{1}{2}(-g)t^2\\ H&=\frac{1}{2}gt^2\\ \end{aligned} $$ $$ \begin{aligned} t&=\sqrt{\frac{2H}{g}} \end{aligned} $$ $$ \begin{aligned} v&=\frac{S}{t}\\ &=\frac{S}{\sqrt{\frac{2H}{g}}}\\ &=S\sqrt{\frac{g}{2H}}\\ &=(14)\sqrt{\frac{g}{2(40)}}\\ &=\frac{7}{2} \sqrt{\frac{g}{5}}\\ &=\frac{7 }{200}\sqrt{\frac{196133}{10}}\ut{m/s}\\ &\approx 4.901662218064399\ut{m/s}\\ &\approx 4.9\ut{m/s}\\ \end{aligned} $$