On one railway line, a train driver begins braking at a yellow signal, which is $1.0\,\text{km}$ before a red signal at which the train comes to rest. The train’s greatest deceleration is $0.20\,\text{m s}^{-2}$. If the deceleration is constant, what is the highest safe speed of the train at the yellow signal?
- A$14\,\text{m s}^{-1}$
- B$20\,\text{m s}^{-1}$
- C$40\,\text{m s}^{-1}$
- D$400\,\text{m s}^{-1}$