Math help please!
A firecracker shoots up from a hill 140 feet high, with an initial speed of 100 feet per second. Using the formula H(t) = -16t2 + vt + s, approximately how long will it take the firecracker to hit the ground? (4 points)
Five seconds
Seven seconds
Nine seconds
11 seconds

- anonymous

- jamiebookeater

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- anonymous

- anonymous

i think the answer is 7 seconds

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## More answers

- anonymous

Okay so here you have your equation
H(t) = -16t2 + vt + s
You are given the initial height = 140 = s
And the initial speed = v = 100 ft/s
16 t^2 + 100 t + 140 = H(t)
Since you want to find the time it took to hit the ground, you are looking for the x intercept. Set the equation equal to 0 then use the quadratic formula.
16 t^2 + 100 t + 140 = 0

- anonymous

ok i understand that but im unsure of how to solve it

- anonymous

Do you know the quadratic formula?

- anonymous

yes, so i would just use that?!!!

- anonymous

Yes. DO you see how the formula resembles a quadratic. The only difference is that it is a t and not an x

- anonymous

You should get 6.53. That rounds to 7.

- anonymous

-16 t^2 + 100 t + 140 = 0
I forgot the negative.

- anonymous

ok yes i got that answer thanks so much!!!!!!! ;)

- anonymous

No problem!!

- anonymous

do you mind helping with one more?

- anonymous

Darlene kicks a soccer ball off the ground and in the air, with an initial velocity of 34 feet per second. Using the formula H(t) = -16t2 + vt + s, what is the maximum height the soccer ball reaches? (4 points)
17.7 feet
18.1 feet
19.3 feet
20.2 feet
Im getting 17.7 feet?

- anonymous

Sure

- anonymous

height + velocity + gravity
https://www.youtube.com/watch?v=K7b-da1o3BY

- anonymous

Well what do you know? What is your initial velocity and initial height?

- anonymous

the velocity is 34 feet and i believe the unital height is 0 feet

- anonymous

assuming since the problem doesnt say

- anonymous

for the height

- anonymous

Yup. So plug them into the equation for v and s

- anonymous

H(t) = -16t2 + 34t + 0

- anonymous

yes so the answer would be 18.1 feet ??

- anonymous

Yeah!

- anonymous

Thanks so much for walking me through it!!!!!!!

- anonymous

You're welcome (:

- anonymous

Medal?

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