12-42 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} L&=6.2\ut{m}\\ mg&=400\ut{N}\\ \mu&=0.39\\ \end{cases} $$ $$ \begin{cases} \Sigma F_{x}&=0\\ \Sigma F_{y}&=0\\ \Sigma \tau&=0\\ \end{cases} $$ $$ \put\begin{cases} F=\text{Force Wall}\\ N=\text{Force Floor}\\ h=\text{Wall Distance}\\ x=\text{Floor Distance}\\ \end{cases} $$ $$ h=\sqrt{L^2-x^2} $$ $$ \begin{cases} 0&=F-\mu N\\ 0&=N-mg\\ 0&=-\frac{x}{2}mg+xN-h\mu N\\ \end{cases} $$ $$ \begin{aligned} x&=\frac{2 \mu L}{\sqrt{4 \mu ^2+1}}\\ &=\frac{1209}{5 \sqrt{4021}}\ut{m}\\ &\approx 3.813197151902038\ut{m}\\ &\approx 3.8\ut{m}\\ \end{aligned} $$