A trolley with mass $4.0\ \text{kg}$ and speed $4.0\ \text{m s}^{-1}$ strikes a trolley of mass $2.0\ \text{kg}$ moving at $2.0\ \text{m s}^{-1}$ in the same direction. Following the collision, the speed of the $4.0\ \text{kg}$ trolley falls to $3.0\ \text{m s}^{-1}$. What is the velocity $v$ of the $2.0\ \text{kg}$ trolley after the collision?
- A$0.25\ \text{m s}^{-1}$
- B$4.0\ \text{m s}^{-1}$
- C$5.0\ \text{m s}^{-1}$
- D$16\ \text{m s}^{-1}$