Question

A firecracker shoots up from a hill 160 feet high with an initial speed of 105 feet per second. Using the formula H(t) = −16t2 + vt + s, determine how long it will take the firecracker to hit the ground.

7.5 seconds

7.8 seconds

8.1 seconds

8.3 seconds

Answer 1

@primeralph

Answer 2

okay, do you know calculus?

Answer 3

Madam is it a Physics question or Mathematics Question ?

Answer 4

the whatever will be at the ground twice: when it leaves and when it falls. So, you will have two answers: the larger one is what you want.
All you have to do is set the equation = 0, but for v, put160

Answer 5

calculus ? no im in algebra 1 @primeralph and math @goformit100

Answer 6

let me see what you can come up with

Answer 7

you don't need calculus for this problem

Answer 8

@nincompoop in real life, stuff don't work out so easily, except in algebra. That's why I asked.

Answer 9

im confused ... what do i do ?

Answer 10

solve for t

Answer 11

@Denebel she doesn't seem much like a physics person to me............

Answer 12

you're going to get a wrong answer if your v is set to 150

Answer 13

...... i get a decimal

Answer 14

yeah, what's it?

Answer 15

10.342 and -0.96694

Answer 16

@primeralph

Answer 17

i think the reasonable one makes sense in that situation.

Answer 18

The formula is H(t) = -16t^2 + 105t+160 = 0 (because v=105 as stated in your problem). You would also want to disregard any negative numbers because it is not possible to have a negative time

Answer 19

errrr, but them answers ain't in the options

Answer 20

If you solve h(t) = -16t^2 + 105t+160, it matches one of the choices (with rounding)

Answer 21

@Denebel , not really.........

Answer 22

.-.

Answer 23

okay we're wasting a lot of time here...

Answer 24

@Gabylovesyou you'll have to go with 10.34.... even though it isn't in the options

Answer 25

@Gabylovesyou summon me to help :) I don't want to be rude by taking over

Answer 26

@poop, do your thing, time is running out.

Answer 27

You need to use the quadratic formula \[\frac{ -b \pm \sqrt{b ^{2}+4ac} }{ 2a } = \frac{ -105\pm \sqrt{105^{2}-4(-16)(160} }{ 2(-16) }\] Plug this in your calculator. You will get a positive and negative answer. then disregard the negative one

Answer 28

@goformit100: its a dynamics question :)

Answer 29

you know this requires several steps and one other solution is to use the quadratic formula

set H(t) to 0
therefore you will have the formula
0 = -16t^2 + 105t+160
since you have a negative as your leading coefficient, you need to first multiply both sides by -1 giving you
0 = 16t^2 - 105t -160
then use the quadratic formula.
this also can be solved by completing the square.

Answer 30

oh, twas 105 not 150........ either way the answer ain't in the options

Answer 31

ya I told you from the start that you will get the wrong answer if you set your v to 150

Answer 32

-16 t^2+105 t+160 = 0
Multiply both sides by a term to make the coefficient of t^2 positive.
Multiply both sides by -1:
16 t^2-105 t-160 = 0
Using the quadratic formula, solve for t.
t = (105±sqrt((-105)^2-4×16 (-160)))/(2×16) = (105±sqrt(11025+10240))/32 = (105±sqrt(21265))/32:
Answer: |
t = (105+sqrt(21265))/32 or t = (105-sqrt(21265))/32

Answer 33

As @Denebel said , Use quadratic formula ...
Remember that the answer will be only da posivtive value

Answer 34

Positive *

Answer 35

but since w're talking about time here and time doesn't go back, unless you want to be Einstein, then obtain the positive value.

Answer 36

whats the answer?

Answer 37

plug into your calculator

Answer 38

http://www.wolframalpha.com/input/?i=0+%3D+-16t%5E2+%2B+105t%2B160

Answer 39

do you know how to complete the square yet, @Gabylovesyou

Answer 40

−16t2 + 105t + 160 = 0
@Gabylovesyou please solve, as you solved earlier.

Answer 41

don't forget the caret sign, @primeralph
^ ^ ^ ^ ^ ^ ^ called caret

Answer 42

WUT? is it C?

Answer 43

the answer is in the option when it is rounded off to the first decimal

Answer 44

it has to be in the answers ... .-.

Answer 45

@nincompoop is it C?

Answer 46

no, poop is right, it is among them.

Answer 47

look at this link and tell me if you see http://www.wolframalpha.com/input/?i=0+%3D+-16t%5E2+%2B+105t%2B160
the value very close to the one of the options

Answer 48

@Gabylovesyou what type of calculator do you use?

Answer 49

is it B ?

Answer 50

@primeralph i use wolfram

Answer 51

yeah, B. I mean handheld.

Answer 52

lol finally! ITS B!!!!!!!!!!!!!! right @nincompoop