Need some "math" help!!!!!

[DonnaL]

Before I throw this book across the room and break my favorite knick-knack...
http://seedonna4designs.com/banghead.gif

If ANYONE knows Algebra at all ... please... I can't find any answers and I can't get any help off my dang instructor!! She hasn't answered any of my emails and my assignment is due tomorrow.... I have tons and tons of links to websites about this particular equation but I am SOOO dang lost on one particular aspect of it.

What I'm trying to do is quadratic functions...... (whatever that means) and the example shows this....

When thrown into the air from the top of a 50 ft building, a ball’s height, S, at time t can be found by S(t) = -16t^2 + 32t + 50. When t = 1, s = -16(1)^2 + 32(1) + 50 = 66. This implies that after 1 second, the height of the ball is 66 feet. When t = 2, s = -16(2)^2 + 32(2) + 50 = 50. This implies that after 2 seconds, the height of the ball is 50 feet.
Question........ in the equation... where did they get the -16 from? (ones in bold)

I'm seeing this in my text book with their examples like this...
Food Stamp Program.. blah blah blah... Over half of all participants are children; one out of six is a low income older adult. The function f(x) = 0.22x^2 - 0.50x + 7.68...... where did they get 0.22 from????

[hewligan]

They made it up.

No, really.

A quadratic equation is any equation of the form ax^2 + bx + c = d [or (x + e)(x + f) - you can convert between the two ways of writing a quadratic equation], where a, b, c, d, e and f are some numbers, and x is your variable for the equation. So if this were real life, those numbers in your example equation would have come from the actual motion of the ball, chosen to describe the path the ball is following. But, since this is an example in a text book, they just picked some numbers.

[DonnaL]

too late.... book was thrown across the room! LOL....

Seriously.... I just don't get it... I gave up.... I posted in another thread that I got an A in my last assignment...... I pretty much "copied" the example from the book and plugged in the assignment numbers... *shrugs*... so do I get any of this... heck no...

Therefore... I'm gonna flunk this class because I can't find proper help... I need to be with someone in real life to sit with me and work through these with me...

Thanks..... but I'm giving up.

[Navian]

too late.... book was thrown across the room! LOL....

Seriously.... I just don't get it... I gave up.... I posted in another thread that I got an A in my last assignment...... I pretty much "copied" the example from the book and plugged in the assignment numbers... *shrugs*... so do I get any of this... heck no...

Therefore... I'm gonna flunk this class because I can't find proper help... I need to be with someone in real life to sit with me and work through these with me...

Thanks..... but I'm giving up.

Does your school, have tutors?

I'd advise using them (sometimes they are free, sometimes you pay for them, but they are worth it). Instructors are busy preparing lessons, checking homework, etc.. Tutors are there to help students with understanding subjects you are having problems with.

Go to your L.R.C. (Learning Resource Center / AKA Library), they should be able to help you. No offense but there is no excuse for flunking a class.

[DonnaL]

yeah, we have tutors but they are all booked. Every resource and reference and website isn't telling me where that number comes from....

One girl posted her equation and I asked her where she got her number from. Her's was throwing a football across the room or something like that... I asked her where she got the number from and she said it was the size of the football... **shrugs** ... what baffles me is that the example given by the instructor says a rock thrown from a building - the number used is -16... how can that be the "size" of the rock???

[Two-Toe Tom]

the numbers come from the motion you're trying to model. for example, if you were given the position, velocity and acceleration at a certain time, then that would determine the coefficients. you would do this using some basic calculus, but it seems you're not required to know that, so i'd just treat the numbers as a given and not worry about them.

are there any questions where they ask you to determine the coeffecients of the equation?

[DonnaL]

what's a coeffecient?

Bloody hell! I took Algebra 25 years ago in High school, and I'm suppose to remember it?

Another student just told me that the -16 in the above equation is the gravitational pull from the earth's gravity! That can't be right! Other students have used 3... another student used 5.....

This is only part of my assignment....
Part 2: Using the Library, web resources, and/or other materials, find a real-life application of a quadratic function. State the application, give the equation of the quadratic function, and state what the x and y in the application represent. Choose at least two values of x to input into your function and find the corresponding y for each. State, in words, what each x and y means in terms of your real-life application. Please see the following example. Do not use any version of this example in your own post. You may use other variables besides x and y, such as t and S depicted in the following example. Be sure to reference all sources using APA style.


Typing hint: To type x-squared, use x^2. Do not use special graphs or symbols because they will not appear when pasted to the Discussion Board.

When thrown into the air from the top of a 50 ft building, a ball’s height, S, at time t can be found by S(t) = -16t^2 + 32t + 50. When t = 1, s = -16(1)^2 + 32(1) + 50 = 66. This implies that after 1 second, the height of the ball is 66 feet. When t = 2, s = -16(2)^2 + 32(2) + 50 = 50. This implies that after 2 seconds, the height of the ball is 50 feet.

[Two-Toe Tom]

the coefficient is the number in front of the variable (in this case, the coefficients are -16, 32 and 50. your friend is right about the -16, using calculus, the acceleration of your equation is -32 ft/s/s, which is what earth's gravitation pull gives. the negative means its accelerating in a downwards motion.

looks like you don't need to say what the numbers represent, just what s and t represent. in this case, s represents the vertical position, in feet, of the ball as measured from the ground. s represents the time, in seconds, after the ball is thrown.

[DonnaL]

Ok.... so why did some students use a different number other than -16? Are they "wrong"?

[Two-Toe Tom]

it depends on the motion they're modelling. if they're modelling a free falling object in earth's gravity, then it should be -16 (or -4.9 if you're using the metric system). if they're modelling something else, then it would have a different number.

[DonnaL]

One used a child's nerf football and used 5
Some did something else and used 3

[Two-Toe Tom]

i dunno, i personally never worried that much about what other ppl did. if their object is falling, then it should be a negative number (assuming up is positive).

[DonnaL]

I"m looking at their posts so I can try to put it together and see how it's done... whether I know if they're right or not.. I dunno....

We also have to post responses to these other students equations as well and believe me, I'm asking ALL of them....... where did you get that number from??

[Two-Toe Tom]

the first number comes from the acceleration of the motion. in general, given a function representing a position, s=Ax^2+Bx+C, the acceleration is 2A (using calculus).

[DonnaL]

If I throw my math book across the room how long will it take to hit the ground?
Using a stop watch…. 2 secs.
Where I’m standing: l = living room
Where it lands: k = kitchen
D = distance – 10 feet
H = height – 5 feet
***shrugs***

Can I make an equation out of that??

[Two-Toe Tom]

you need to make equations for the vertical position and the horizontal position.

horizontal position is just a linear equation, in this case, Sx=5t.

vertical position, you know the -16 part cuz that's from the gravitational acceleration, so you get:

Sy=-16t^2+Bt+C

assuming your H=5ft is your starting position, then you get

Sy(0)=-16(0)^2+B(0)+C=5, so C=5

and since it hits the ground after 2 seconds,

Sy(2)=-16(2)^2+B(2)+5=0, so B=29.5

so Sy=-16t^2+29.5t+5

where you're standing and where it lands are irrelevant to the motion.

[DonnaL]

Ok so if I stand on the roof of my house... and then toss it over the edge?

What does the B represent?

My head is spinning!!

[Two-Toe Tom]

its the same process if you toss if from the roof of your house, just the time it hits the ground and the initial height is different. B is the initial velocity. at what rate is your head spinning? and in which direction?

[DonnaL]

well since my brain isn't functioning properly on the "left" side.. my head is spinning clockwise and at a rate of 100mph

[Two-Toe Tom]

actually, the rate at which your head is spinning should be given in # of revolutions per unit time :p

[DonnaL]

don't I have to calculate the width of my head to verify the time of one revolution around? The bigger the slower.. the smaller the faster???

[Two-Toe Tom]

yes, in general, bigger things spin more slowly due to a larger moment of inertia. as for measuring how fast your head is spinning, i'd just pick an object in the room and count how many times you see it go by in a minute, and that would give you your spin rate in revs/minute.

[DonnaL]

you ever see something spin so fast it looks like it's standing still?

That's me........

[Two-Toe Tom]

ah yes, the strobe effect. assuming you're indoors and indoor lighting flickers at 60hz, your head is probably spinning at a rate of 60revs/second or a multiple of that.

[DonnaL]

sounds about right..... and it better stop soon or I'll be mimicking The Exorcist

[Two-Toe Tom]

get someone to sit on your head and someone else to sit on your body, that should do the trick. or use duct tape.

[DonnaL]

Duct tape is out.... will mess up my hair...

[Two-Toe Tom]

well if u have hair u can always tie it to a post

[DonnaL]

LOL... true... but my hair is short!!

Anyway..... calling this week a flop.... maybe next week's assingment will be a little easier to comprehend.. it's something different. We'll see. Can't think, can't comprehend this and I'm literally feeling sick to my stomach will it all.... time to go do soemthing else OTHER than math....

this weeks grade? F

[GraphixNPrint]

Donna drink a beer or 12 and recalculate the head spinning. This should help you answer the initial question. :)

[urstwile]

This entire thread needs to be posted in the next QOTW. :D