Algebra Demystified 2nd Ed

Chapter 11 QuaDraTiC appliCaTionS 415

–+ 16 tt  = 25  = 00  ( Thisiswhentheobjectisthhrown.

–= –

= –

• = 

= 

)

 .

16 25

25

16

25

16

1 5625

t

t

t

t

The object will hit the ground after 1.5625 seconds.

2. In the formula h = −16t^2 + v 0 t + h 0 , v 0 = 150 and h 0 = 0.

h = −16t^2 + 150t

We want to find t when h = 0.

016 150

016 150

16 150 0

2

 (  )

= –+

=  –+

–+ =

tt

tt

tt =  (.Thisiswhen theprojectileisfired)

• 
  

0

16 tt

t

t

t

 .

= –

= –

• = 
  = 

150

150

16

75

8

9 375

The object will fall back to the ground after 9.375 seconds.

3. In the formula h = −16t^2 + v 0 t + h 0 , v 0 = 20 and h 0 = 50.

h = −16t^2 + 20t + 50

We want to find t when h = 55.

55 = −16t^2 + 20t + 50

0 = −16t^2 + 20t − 5

t  ()()( )

()

= –± –  ––

• 
  

(^20204165) = –± – 
216
(^2204003220)
32
20 80
32
20 894
32
035090

• = –±


• 
  

  ≈ –±

  
  


• 
  

≈ 

.  ., .