Question

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

Answer 1

@gina123 @gina123

Answer 2

@Michele_Laino @ganeshie8

Answer 3

i think the answer is 7 seconds

Answer 4

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

Answer 5

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

Answer 6

Do you know the quadratic formula?

Answer 7

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

Answer 8

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

Answer 9

You should get 6.53. That rounds to 7.

Answer 10

-16 t^2 + 100 t + 140 = 0

I forgot the negative.

Answer 11

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

Answer 12

No problem!!

Answer 13

do you mind helping with one more?

Answer 14

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?

Answer 15

Sure

Answer 16

height + velocity + gravity

https://www.youtube.com/watch?v=K7b-da1o3BY

Answer 17

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

Answer 18

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

Answer 19

assuming since the problem doesnt say

Answer 20

for the height

Answer 21

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

Answer 22

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

Answer 23

yes so the answer would be 18.1 feet ??

Answer 24

Yeah!

Answer 25

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

Answer 26

You're welcome (:

Answer 27

Medal?