A car with mass $1000\,\text{kg}$ moving at $8.0\,\text{m s}^{-1}$ hits a lorry with mass $3000\,\text{kg}$ moving at $2.0\,\text{m s}^{-1}$ in the same direction. After the collision, the two vehicles remain attached. What speed do they have after the collision?
- A$2.0\,\text{m s}^{-1}$
- B$2.5\,\text{m s}^{-1}$
- C$3.5\,\text{m s}^{-1}$
- D$5.0\,\text{m s}^{-1}$