410 algebra De mystif ieD
t^2 =^70
16
t^235
8
= ^
t =^35
8
t ≈ 2.09
The ball will hit the ground in about 2.09 seconds.
- For the formula h = –16t^2 + v 0 t + h 0 , h 0 = 100 and v 0 = 0 (because the
object is being dropped). The object reaches the ground when h = 0.
h = –16t^2 + 100
0 = –16t^2 + 100
16 t^2 = 100
t^2 =^100
16
t^2 =^25
4
t =^5
2
t = 2.5
The object will hit the ground after 2.5 seconds.
We now work with finding the length of time it takes for an object to reach
a certain height after being dropped. We let h represent the height in
question.
EXAMPLE
An object is dropped from the roof of a 60-foot building. When will it reach
a height of 28 feet?
In the formula h = –16t^2 + v 0 t + h 0 , h 0 is 60 and v 0 is zero (because the object
is dropped). The object reaches a height of 28 feet when h = 28.
h = –16t^2 + 60
28 = –16t^2 + 60
16 t^2 = 32
EXAMPLE
An object is dropped from the roof of a 60-foot building. When will it reach
a height of 28 feet?
EXAMPLE
An object is dropped from the roof of a 60-foot building. When will it reach