12-17 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} d&=60\ut{m}\\ L&=150\ut{m}\\ H&=7.2\ut{m}\\ z&=5.8\ut{m}\\ A&=885\ut{cm^2}\\ \rho&=2.8\ut{g/cm^3}\\ S_{\text{steel}}&=400\times10^6\ut{N/m^2} \end{cases} $$ $$\ab{a}$$ $$ \begin{aligned} \Ans&=mg\\ &=\rho V g\\ &=\rho L d z g\\ &=1.4616\times10^8\ut{N}\\ &\approx 1.5\times10^8\ut{N}\\ &\approx 150\ut{MN}\\ \end{aligned} $$ $$\ab{b}$$ $$ \begin{aligned} {F \over NA}&={1\over2}S_{\text{steel}}\\ \end{aligned} $$ $$ \begin{aligned} N &={2F \over AS_{\text{steel}}}\\ &={2436g \over 295}\\ &\approx 80.97965898305085\\ &\approx 81\\ \end{aligned} $$