5-4 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} mg&=860\ut{N}\\ \vec a&=-a\\ a&=2.40\ut{m/s^2}\\ g&=9.80665\ut{m/s^2} \end{cases} $$ $$\ab{a}$$ $$ \begin{aligned} \Sigma \vec F &= m\vec a,\\ F-mg&=-ma\\ \end{aligned} $$ $$ \begin{aligned} F&=m(g-a)\\ &\approx 649.5305736413557\ut{N}\\ &\approx 6.50\times10^2\ut{N}\\ \end{aligned} $$ $$\ab{b}$$ $$\title{Up}$$ $$\ab{c}$$ $$F_{AB}=-F_{BA},$$ $$ \begin{aligned} F&=m(g-a)\\ &\approx 649.5305736413557\ut{N}\\ &\approx 6.50\times10^2\ut{N}\\ \end{aligned} $$ $$\ab{d}$$ $$\title{Down}$$