#### Answer

8 seconds

#### Work Step by Step

We are given in Example 5 that the height of an object at t seconds can be found by the equation $P(t)=-16t^{2}+1125$. To find how long it takes before the object hits the ground, we must find the time t, such that $P(t)=0$.
$P(t)=-16(t^{2})+1125=0$
$0=-16t^{2}+1125$
Add $-16t^{2}$ to both sides.
$16t^{2}=1125$
Divide both sides by 16.
$t^{2}=70.3125$
Take the square root of both sides.
$t=8.385\approx8$ seconds