Question

Daniel tosses his basketball onto the ground from his second story window.He tosses the basketball with an initial downward velocity of 8 ft. per second.The equation h=-16t^2-8t+20 represents the height h of the basketball after t seconds.How long does the basketball take to hit the ground?

Answer 1

Set the quadratic = to 0 and solve for time, t:

-16t^2 - 8t + 20 = 0

Reduce this to:

-4t^2 - 2t + 5 = 0

 Here a= -4, b= -2 and c =5.  Then,

       2 plus or minus sqrt( 4-4(-4)(5) )
t = ---------------------------------------------
                            -8
        2 plus or minus sqrt(84)
  = ------------------------------------
                          -8

Finish evaluating this.  If either outcome is negative, discard it.
The result will be the number of seconds required for the ball to hit the grnd.