A.
[tex]\begin{gathered} Momentum \\ m1v1+m2v2=m1v3+m2v4 \\ (100\cdot200)+0=(100\cdot-120)+(400\cdot v4) \\ 20000=-12000+400v4 \\ 32000=400v4 \\ v4=80cm/s \end{gathered}[/tex]This is momentum conservation, is important to maintain the direction to know the positive and negative values
B.
[tex]\begin{gathered} F=\frac{m(\Delta v)}{\Delta t} \\ F=\frac{0.4kg(0.8m/s)}{0.1s} \\ F=3.2N \end{gathered}[/tex]For this part, is important to use the correct units. On A it was not relevant because you can use any units, you only have to maintain them the same.
