Question

You are walking on a bridge and accidentally drop your cell phone. If the bridge is 45.4 m above the water, how long does it take the phone to hit the water?

Answer 1

the cell phone will start out at rest. after 1 second it will have gone 9.81/2[m]. Two seconds later it will have been displaced a total of 2*9.81[m]. Three seconds it will have gone 22.07[m]. Four seconds it will have gone 78.48 meters.

So some time between t=3s and t=4s but where exactly?
some clues...
In general;
\[Displacement=\frac{ 1 }{ 2 }at ^{2}\]

near earths surface a=g[m/s^2]