9-4 할리데이 11판 솔루션 일반물리학

$$\begin{cases} m_A&=0.270\ut{kg}\\ \vec v_{\text{in}}&=-12.0\j\ut{m/s}\\ \vec v_{\text{out}}&=+3.00\j\ut{m/s}\\ \vec v_B&=0 \end{cases}$$ $$\ab{a}$$ $$\begin{aligned} \Delta \vec P_A&=\Delta (m_A\vec v_A)\\ &=m_A\Delta \vec v_A\\ &=m_A (\vec v_{Af}-\vec v_{Ai})\\ &=m_A (\vec v_{\text{out}}-\vec v_{\text{in}})\\ &=\frac{81}{20}\j\ut{kg\cdot m/s}\\ &=4.05\j\ut{kg\cdot m/s}\\ \end{aligned}$$ $$\ab{b}$$ $$\begin{aligned} \vec J_A&=\Delta \vec P_A\\ &=4.05\j\ut{N\cdot s}\\ \end{aligned}$$ $$\ab{c}$$ $$\begin{aligned} \vec J_B&=\vec J_A\\ &=4.05\j\ut{N\cdot s}\\ \end{aligned}$$