9-3 할리데이 11판 솔루션 일반물리학

$$\begin{cases} m_A&=75\ut{kg}\\ m_B&=50\ut{kg}\\ v_i&=2.3\ut{m/s}\\ v_{Af}&=0 \end{cases}$$ $$\Delta \Sigma \vec P=0,$$ $$\begin{aligned} \vec P_i&=\vec P_{Af}+\vec P_{Bf}\\ (m_A+m_B)v_i&=m_Av_{Af}+m_Bv_{Bf}\\ &=m_Bv_{Bf}\\ \end{aligned}$$ $$v_{Bf}=\frac{m_A+m_B}{m_B}v_i$$ $$\begin{aligned} \Delta v_B&=v_{Bf}-v_{Bi}\\ &=\frac{m_A+m_B}{m_B}v_i-v_{i}\\ &=\frac{m_A}{m_B}v_i\\ &=+\frac{69}{20}\ut{m/s}\\ &=+3.45\ut{m/s}\\ &\approx +3.5\ut{m/s}\\ \end{aligned}$$