Question

A firecracker shoots up from a hill 145 feet high with an initial speed of 80 feet per second. Using the formula H(t) = -16t2 + vt + s, approximately how long will it take the firecracker to hit the ground?

Answer 1

Well first off we have to understand what each of the variables mean in the equation they give us

Answer 2

\[H(t) = -16t^2 + v t + s\]

"t" is time

The "H(t)" is read "H of t" and just means that "if we plug in a time this is the height of the firecracker"

"v" is the initial velocity

"s" is the initial starting height

Answer 3

Oh, that helps! Thanks for clearing that up.

Answer 4

the value of H at ground level = 0
0 = - 16t^2 + 80t + 145
solve this for t

i'm not 100% sure of this eyust will probably know for sure

Answer 5

yea no problem! thats why I come on here =P

And yes I agree with cwrw.

v = 80
s = 145
And we want to solve for time when H(t) is 0

Answer 6

So it's t=6?

Answer 7

yea its close to 6...

Answer 8

did you use the quadratic equation?

Answer 9

http://www.wolframalpha.com/input/?i=0+%3D+-+16t^2+%2B+80t+%2B+145&dataset=

Answer 10

theres a graph of the flight pattern with respect to time =P

Answer 11

Thanks a lot!!

Answer 12

notice that the positive root is close to 6 but not quite..

Answer 13

yea no problem

Answer 14

Yeah, but I'll just round.

Answer 15

i probably would too.. maybe like 2 or 3 sig figs.??

Answer 16

Good idea, thanks again!