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The equation y = -16t^2 + 28t + 144 describes the height (in feet) of a ball tossed up in the air at 28 feet per second from a height of 144 feet from the ground. In how many seconds will the ball hit the ground?

 Jan 17, 2020
 #1
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When it hits the ground, y  = 0....so....

 

-16t^2  + 28t  + 144  = 0        divide through by  -4

 

4t^2 - 7t  - 36  =  0       factor

 

(4t  + 9) ( t - 4)  = 0

 

Only the second factor  will produce a positive value for t

 

So

 

t  - 4  =   0

 

t  = 4 sec

 

 

 

cool cool cool

 Jan 17, 2020

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