The initial speed of a projectile fired from ground is \( u \). At the highest point during its motion, the speed of projectile is \( \frac{\sqrt{3}}{2}u \). The time of flight of the projectile is:
\( \frac{u}{g} \)
\( \frac{\sqrt{3}u}{g} \)
\( \frac{2u}{g} \)
\( \frac{u}{2g} \)