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The height h (in feet) of an object t seconds after it is dropped can be modeled by the quadratic equation 
h = -16t^2 + h0, where h0 is the initial height of the object. Suppose a small rock dislodges from a ledge that is 255 ft above a canyon floor. Solve the equation h = -16t^2 + 255 for t, using the quadratic formula to determine the time it takes the rock to reach the canyon floor.

Guest Mar 27, 2017
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When it hits the ground, h  = 0  ....so we have

 

0  =  -16t^2  + 255      we could use the quad formula, but this approach is faster

 

add  16t^2 to both sides

 

16t^2   = 255      divide both sides by 16

 

t^2  =   255/16       take the positive root of both sides

 

t  = sqrt (255 /16)   ≈   4 seconds

 

 

cool cool cool

CPhill  Mar 27, 2017

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