If a baseball player hits a baseball from 4 feet off the ground with an initial velocity of 64 feet per second, how long will it take the baseball to hit the ground? Use the equation h = -16t2 + 64t + 4.

Question

welshfella · Answer

when the ball hits the ground h will = 0
so form an equation and solve for t

anonymous · Answer

So far I have this 64 +/- sqrt 3840 over 32. But I don't know what to do after that

welshfella · Answer

make it easier by taking out -4
-4(4t^2 - 16t - 1) = 0

now apply quadratic formula to the expression in the parentheses

t =[ 16 +-  sqrt(256 - 4*4 * -1) ]  /   8

welshfella · Answer

t = (16 + 16.49)  / 8      (neglect the negative root)

anonymous · Answer

im confused

welshfella · Answer

haven't you used the quadratic formula before?

anonymous · Answer

yes but I didn't get what you got

welshfella · Answer

i applied it to 4x^2 - 16x - 1 = 0

welshfella · Answer

- smaller numbers

anonymous · Answer

oh ok

welshfella · Answer

i divide through by -4 to make it easier

welshfella · Answer

this equation will have the same roots as the bigger one

anonymous · Answer

so the answer I got was 16+/- sqrt 17 over 2 is that what you got?

welshfella · Answer

(16 + sqrt272 ) / 8  = 4.06 secs

anonymous · Answer

my answer has to be in the quadratic formula

welshfella · Answer

oh ok

so that's   (16 +   sqrt(16*17) ) /  8

 = 16 + 4*sqrt17
     -----------
            8

= 2 + 0.5 sqrt17

anonymous · Answer

ok thank you

welshfella · Answer

yw