The car A has a weight of 4500 lb and is traveling to the right at 3 ft/s. Meanwhile a 300...

Fred body diagram

Conservation of linear momentum

$$ \begin{aligned} &(+) m_{A}\left(v_{A}\right)_{1}+m_{B}\left(v_{B}\right)_{1}=\left(m_{A}+m_{B}\right) v_{2} \\ &\frac{W_{A}}{g}\left(v_{A}\right)_{1}-\frac{W_{B}}{g}\left(v_{B}\right)_{1}=\left(\frac{W_{A}}{g}+\frac{W_{B}}{g}\right) v_{2} \\ &v_{2}=\frac{4500 \times 3-3000 \times 6}{4500+3000} \\ &v_{2}=-0.6 \mathrm{~m} / \mathrm{s} \end{aligned} $$