A railway engine speeds up a train with a total mass of $1200$ tonnes ($1\,\text{tonne} = 1000\,\text{kg}$), taking it from rest to $75\,\text{m s}^{-1}$. How much useful work has to be done on the train for it to reach this speed?
- A$3.4 \times 10^6\,\text{J}$
- B$6.8 \times 10^6\,\text{J}$
- C$3.4 \times 10^9\,\text{J}$
- D$6.8 \times 10^9\,\text{J}$