5-46 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} F_1&=4500\ut{N}\\ a_1&=0\\ \end{cases} $$ $$ \begin{cases} F_2&=2600\ut{N}\\ a_2&=-0.39\ut{m/s^2}\\ \end{cases} $$ $$\ab{a}$$ $$\Sigma \vec F = 0 \Harr \Delta \vec v=0,$$ $$ \begin{aligned} \Sigma F_1 &= 0\\ F_1-mg &= 0\\ mg&=F_1\\ &=4500\ut{N} \end{aligned} $$ $$\ab{b}$$ $$\Sigma \vec F = m\vec a,$$ $$ \begin{aligned} \Sigma F_2 &= m a_2\\ F_2-mg &= m a_2\\ \end{aligned} $$ $$ \begin{aligned} m&=\frac{F_2-F_1}{a_2}\\ &=\frac{190000}{39}\ut{kg}\\ &\approx 4871.794871794872\ut{kg}\\ &\approx 4.9\times10^3\ut{kg}\\ &\approx 4.9\ut{ton}\\ \end{aligned} $$ $$\ab{c}$$ $$F = m\vec g,$$ $$ \begin{aligned} g&=\frac{F_1}{m}\\ &=\frac{4500}{\frac{190000}{39}}\ut{m/s^2}\\ &=\frac{351}{380}\ut{m/s^2}\\ &\approx 0.9236842105263158\ut{m/s^2}\\ &\approx 0.924\ut{m/s^2}\\ \end{aligned} $$