A stone is released from rest and falls vertically downward. Air resistance is negligible. Determine the speed of the stone after it has dropped a distance of $0.40\,\text{m}$?
- A$2.0\,\text{m s}^{-1}$
- B$2.8\,\text{m s}^{-1}$
- C$3.9\,\text{m s}^{-1}$
- D$7.8\,\text{m s}^{-1}$