Question

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?

Five seconds
Seven seconds
Nine seconds
11 seconds

Answer 1

@ganeshie8 @Abhisar

Answer 2

@hartnn

Answer 3

yeah I already did that.

h(t) = -16t^2 + 100t + 140

Answer 4

D.

Answer 5

I am pretty sure it is not seven seconds though

Answer 6

and @DanteFemboy do you know why its D?

Answer 7

then set it equal to zero

Answer 8

solve h(t) =0
-16t^2 + 100t + 140= 0

Answer 9

you have to use quadratic formula

Answer 10

t = 7.42 , -1.18

we can reject the negative solution

Answer 11

If my calculator is right i solved it to be 140. And what goes into 140 evenly? 11.83215957. So mostly 11. Is that right @perl if not then I need to update my stuff.

Answer 12

I think i'm wrong. Big time lol.

Answer 13

you must set it equal to zero :)

Answer 14

But you have to move the X to one side right?

Answer 15

One second

\[t= −b (+ or −) (√b2−4ac)\div2a\] right?

Answer 16

you mean t, it is already moved to one side

Answer 17

Well yeah t. Ah I know what I messed up on lol

Answer 18

ok so t = 7.4
t = -1.17

Answer 19

h(t) = -16(7.4)^2 + 100(-1.17) + 140

right?

Answer 20

and you shouldnt plug in different t values, they are separate solutions

Answer 21

I'm confused, since I found t, what do I do with it now?

Answer 22

youre done, now you know how long it will take to hit the ground

Answer 23

you have your time. but the negative solution you can ignore

Answer 24

wait I think I get it now. So, it will take 7 seconds?

Answer 25

yes

Answer 26

Oh! Sorry I am usually good with this but I can't think today and I am extremely tired. Lol thank you! :)

Answer 27

:)