A girl throws a ball straight upwards. The ball takes $3.20\,$s to come back to her hand. Assume air resistance can be ignored. What is the initial speed at which the ball is thrown?
- A$3.07\,\text{m s}^{-1}$
- B$7.85\,\text{m s}^{-1}$
- C$15.7\,\text{m s}^{-1}$
- D$31.4\,\text{m s}^{-1}$