Algebra Demystified 2nd Ed

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.

4. 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