Question

Captain hook orders peter pan to walk the plank from which he falls into the sea 18m below. Peter pan claims that his life flashed before his eyes during his fall. How much time is available for this?

Answer 1

You would use
d = v0*t + 0.5at^2
Solve for t. v0 is 0, d is 18 and a is -9.81

t = sqrt(18/4.9)

Answer 2

The distance fallen through gravity in ' t ' seconds is

        Distance  =  (1/2) (acceleration of gravity) (t²)

           18 meters  =  (1/2) · (9.8 m/s²) · (t²)

Divide each side by (4.9 m/s²):

                           (18 m) / (4.9 m/s²)  =  t²

                                 3.67 sec²  =  t²

Square root each side:    1.92 sec  =  t  .    (rounded) 

That's not much time.  But Peter Pan never got old, so
presumably he hasn't got too much life to flash through. 
He may be OK with 1.92 seconds.  Maybe even enough
time to linger momentarily over some of the juicier parts.