A projectile is shot straight upward from the ground with a velocity of 64 feet per second. How many seconds will it take to come back and land on the ground?

Answer 1

In feet,

h(t) = -16t² + 64t

It reaches the ground when h(t)=0.

-16t² + 64t = 0

-16t(t - 4) = 0

t = 0 or 4

t=0 is the moment of launch, so it reaches the ground after 4 seconds.