Expert: Scott A Wilson - 11/3/2009

Question
Gravity. A person holds a pistol straight upward and fires. The initial velocity of most bullets is around 1200 ft/second. The height of the bullet is a function of time and is decribed by
h(t)= -16t(squared) + 1200t
How long, after the gun is fired, does the person have to get out of the way of the bullet falling from the sky?

Answer
We are given that h(t) = -16t² + 1200t.
To see when it hits the ground, solve for when h(t) = 0.
That is, solve -16t(t-75) = 0.
When t=0, it is at the ground since it has just started.
The other equation to solve is t-75=0.
Add 75 to both sides and get t=75.
Thus, when t=75, it hits the ground again.