9-56 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} m&=140\ut{g}=0.140\ut{kg}\\ v_i&=9.30\ut{m/s}\\ v_f&=-v_i=-9.30\ut{m/s}\\ \Delta t&=3.80\ut{ms}=3.80\times10^{-3}\ut{s}\\ \end{cases} $$ $$\ab{a}$$ $$ \begin{aligned} \vec J&=\Delta \vec p\\ &=\Delta m\vec v\\ &=m\Delta \vec v\\ &=m (\vec v_f-\vec v_i)\\ &=m (-2\vec v_i)\\ \end{aligned} $$ $$ \begin{aligned} J&=2mv_i\\ &=\frac{651}{250}\ut{N\cdot s}\\ &=2.604\ut{N\cdot s}\\ &\approx 2.60\ut{N\cdot s}\\ \end{aligned} $$ $$\ab{b}$$ $$ \begin{aligned} F&=\frac{\Delta \vec p}{\Delta t}\\ &=\frac{13020}{19}\ut{N}\\ &\approx 685.2631578947369\ut{N}\\ &\approx 685\ut{N}\\ \end{aligned} $$