On a planet, a projectile launched vertically upward takes $12.5\,\text{ s}$ to come back to where it started. Its greatest height is $170\,\text{ m}$. There is no atmosphere on the planet. Determine the acceleration of free fall on this planet?
- A$2.2\,\text{m s}^{-2}$
- B$8.7\,\text{m s}^{-2}$
- C$27\,\text{m s}^{-2}$
- D$54\,\text{m s}^{-2}$