I drop a meter stick, and catch it as it falls. If it fell exactly 22 cm, how much did it take me to catch the meter stick (what was my reaction time) ?

D=Vot+1/2at^2

In this case, there is no initial y velocity so the term Vot=0 so d=1/2at^2

acceleration=acceleration due to gravity=-9.8m/s^2

It falls - 22cm or - 0.22m

We have - 0.22=1/2 (-9.8) t^2

t^2 = (-0.44) / (-9.8)

t=sqrt[0.44/9.8]