If you hold out your hand and drop a penny, about how long does it take to hit the floor?

The equation of motion can be

h (t) = - 16t^2 + 4

for a penny dropped from a height of 4 feet. Then h (t) = 0 for

0 = - 16t^2 + 4

t^2 = 4/16

t = √ (1/4) = 1/2

It takes about 1/2 second for the penny to hit the floor.