# Wikibooks:Study help desk/Archive (April 2007-January 2009)

a distress flare is fired vertically in the aire from a boat at sea. the height in metres of the flare t seconds after firing is given by h=122.5t - 4.9t²

calculate the maximum height reached by the flare. how do you do this. please she working i really need help —The preceding unsigned comment was added by 125.239.27.59 (talkcontribs) 23:30, 24 Apr 2007 (UTC)

First you need to calculate the time at which the rate of change of position (as a function h of t) is equal to 0. To do that, calculate the derivative of h(t) and solve t for h'(t)=0. Then plug the value you get back into the formula h(t)=122.5t - 4.9t². Good luck! --Iamunknown 23:35, 24 April 2007 (UTC)
Well, good luck with that, and there is an alternate way as well, considering that the function you have provided is just a simple parabola of the type y = ax^2 + bx + c. This parabola can always be written as y = a[x+ (b/2a)]^2 - (b/2a)^2 + c. Now, if a>0, Y will be minimum when the only term containing x (the variable) is 0. While, if a<0 y will be maximum when the term is 0. Corresponding to the minimum/maximum, the value of x is then -(b/2a).
Alternatively, compare the equation you have given with ut + (1/2)at^2. It is simply a manipulation of this equation of uniform accelerated motion, with u=122.5 m/s and a=9.8 (m/s)/s. You do know the value of the initial velocity. When the object in question reaches its maximum height, its velocity will be 0, otherwise if non zero the object would rise higher not making that point the highest point. So, find the time when the velocity is 0 using v = u + at, and then, put this value of time in your given equation.
Note - You'll find that on substituting 0 in the last equation mentioned, it morphs into the same equation that is obtained by putting h'(t)=0.
Oh, and well, sorry for my lack of easy language. This reply was written in a haste.

--Thewinster 09:18, 13 September 2007 (UTC)

## Need help in translation. could anyone translate the contextEdit

Subsemnatul ___________, domiciliat in Bucuresti, Calea Victoriei nr. 32-34 sc. A, et. 9, ap. 61, sector 1, nascut la data de 23.08.1945 in Oras Buhusi, jud. Bacau, posesor al CI seria RX nr. 289054 eliberat de Sectia 1 Politie, la data de 01.04.2005, CNP 1450823047797, invite in Romania in scop de VIZITA pentru perioada 10.05.2007-15.07.2007 pe Dna. __________, domiciliata in Filipine, Manila, posesoare a pasaportului nr. SS06334210 eliberat la data de 08.03.2006, valabil pana la data de 08.03.2001, eliberat de autoritatile din Filipine.

Ma oblig sa support cheltuielile legate de intretinere si in caz de inbolnavire sau accident sau de deces pentru porsoana invitata, pe toata perioda sederii in Romania, unde va locui la domiciliul meu. In situatia in care persoana invitata nu va respecta termenul de sedere, ma oblig sa support toate cheltuielile effectuate de autoritatile romane cu privire la aceasta, inclusive cele de transport pentru retrimiterea in tara de origine sau de plecare.

Mentionez ca as dori ca viza pe care o va primi Dna, Violeta F. Del Rosario sa aiba multiple intrari si iesiri, deoarece vrem sa vizitam Ungaria si Bulgaria.

Prezenta invitatie este necesara la Ambasada Romaniei din Manila, Filipine.

Redactat de catre parte, in trei exemplare, din care doua exemplare s-au eliberat patii, iar un exemplar s-a oprit la arhiva biroului notarial.l

You may find a quicker response at w:Wikipedia:Reference desk/Language. I am unable to help. My apologies, Iamunknown 05:45, 29 May 2007 (UTC)

## How to down load a book from wikibooks.Edit

Thanks.

Hi, some books have PDF versions, in which case they have a template which signifies that the book has one. If it doesn't it's somewhat time consuming to make one, but if they have a "Print Version" which contains all of the pages in a book, you can open that and then save it as whatever you want (including a PDF, but printing it to PDF may mess up the formatting so beware. Good luck! Mattb112885 (talk) 23:03, 8 June 2007 (UTC)

## Can't get a TOC on a page I'm editingEdit

Hi! A page I'm editing Feminism/Elizabeth Cady Stanton isn't generating a TOC. What am I not doing properly?--OneWomanArmy923 02:01, 22 June 2007 (UTC)

IIRC, a TOC is not generated until you have N or more headers (N is something like 5). You can force a TOC by including __FORCETOC__ in the page (which I have done for you). --Jomegat 02:06, 22 June 2007 (UTC)
A TOC is automatically generated when you have 4 or more headings. You can use __FORCETOC__ or, more simply, __TOC__ to create one if it isn't appearing automatically. --Whiteknight (Page) (Talk) 03:17, 22 June 2007 (UTC)
Thanks Jomegat. I thought it might take a certain N and now I know. Excellent.--OneWomanArmy923 05:38, 23 June 2007 (UTC)

## how can I purchase (Gods Victorious Army Bible)?Edit

I have a copy of the Spiritual Warfare Reference Edition.The copy that I have has fallen apart I would like to replace it.How can I get a copy did not see a tab where I could purchase this Bible.Help!!!!!!!!!!!!ŷ

You may have more luck at a book selling site such as Amazon or this one. Mattb112885 (talk to me) 22:59, 23 July 2007 (UTC)

## Incomplete tutorialEdit

how do you complete the "Wings 3D: Tutorials: Modeling a generic helicopter", tutorial? i only see the making of the body part. how can i see the rest of the tutorial? —The preceding unsigned comment was added by Dg87 (talkcontribs) 23:28, November 9, 2007.

The tutorial is not yet complete. If you are able, then fix it. If not, then you're out of luck for the moment. Such is the nature of wikis. Mike.lifeguard | talk 02:02, 10 November 2007 (UTC)

## Chemistry homeworkEdit

When an atom absorbs energy, the electrons move from their ground state to an excited state. When an atom emits energy, the electrons move from a(n) excited state to their ground state and give off energy.

Thanks

Sean

Blanks filled in. To find the answers yourself, try A-level Chemistry/OCR (Salters)/Spectroscopy or Emission spectrum (and related articles).  – Mike.lifeguard | talk 02:50, 4 December 2007 (UTC)

## Student-Generated TextEdit

I am completely new to this technology and am diving in head-first to arctic waters! Can anyone provide me with any information about how they use this technology as an educator in the classroom? I'm looking for any history of use of Wikibooks and what you believe the prospects are for it in the future. Thanks!Cmcnulty6497 (talk) 23:52, 12 February 2008 (UTC)

I'm not sure how often Wikibooks are used in the classroom (it would be hard to collect data on this though such data would surely be useful), however, there have been several class projects, in which students work together to write a wikibook. Many of these have gone on to become featured books. As far as prospects for the future, I myself contribute because I hope that it will help low-income students become educated, and I think that (as long as the low-income people have access to a computer) it has the capability of helping in that regard. Mattb112885 (talk to me) 15:44, 13 February 2008 (UTC)

## Limit of a functionEdit

I have a little problem with the limit of the function mentioned below

${\displaystyle \lim _{x\rightarrow 0}{\frac {2\tan x-2\sin x-(x^{3})}{x^{5}}}}$

By writing tanx as sin/cos I am able to get a finite answer, which is 0.5. However, the answerbook says the answer is 0.25. I am unsure how this is so, but I have double checked the problem. If anyone of you here confirms that the answer is indeed 0.5 It'll be a good enough cross check! Thanks! --Thewinster (talk) 08:56, 13 February 2008 (UTC)

Initially I thought as ${\displaystyle \cos x}$  tends to 1 as x tends to 0, the ${\displaystyle 2\tan x}$  would cancel with the ${\displaystyle 2\sin x}$ , giving ${\displaystyle {\frac {-1}{x^{2}}}}$ .
However, from the Taylor series we have:
${\displaystyle \tan x=x+{\frac {x^{3}}{3}}+{\frac {2x^{5}}{15}}+{\frac {17x^{7}}{315}}+...}$
${\displaystyle \sin x=x-{\frac {x^{3}}{6}}+{\frac {x^{5}}{120}}-{\frac {x^{7}}{5040}}+...}$
Substituting in the original formula gives:
${\displaystyle {\frac {2\tan x-2\sin x-(x^{3})}{x^{5}}}={\frac {30}{120}}+kx^{2}+...}$
i.e. As x tends to 0, the higher terms can be ignored giving a result of 0.25. Recent Runes (talk) 19:09, 7 March 2008 (UTC)

## learning disabilities in african americans infoEdit

i am writing a research paper on learning disabilities in african american youth, and am having a hard time finding adequate research material. i have found several articles on adhd a very common type in this community but am having trouble finding info on any others. Please help! --216.26.131.217 (talk) 16:34, 23 April 2008 (UTC)nj

## software engineringEdit

various devolopment models in software enginering? —The preceding unsigned comment was added by Nehru (talkcontribs) 14:52, 12 June 2008 (UTC)

Maybe this is a starting point: Software Engineering? OtherwiseIn any case Help:Searching will be a useful read. --Swift (talk) 14:08, 18 June 2008 (UTC)

## Organic Chemistry HelpEdit

Show the mechanism of 2-butanone from an alkene of your choice? Were can I get the reactions of organic compounds like alkanes, alkenes, alkynes, amides etc... Plzzz help me....

## a little helpEdit

please give me the name of a book through which i might be able to make solar cell of high voltage

## heat enthalpyEdit

hello,um in my school i was not taught calculations in change in heat enthalpy and i would like to learn more especially on the calculation aspect.please could you help me.because i dont understand things by just reading textbooks unless i am taught.

Thanks—Preceding unsigned comment added by Taiwo martins (discusscontribs) 22:18, 23 January 2009

I'm afraid that you've found yourself posting at a reference desk. This is where you ask for help in locating a book on a particular subject; not where you recruit teachers. Maybe your teacher can recommend a qualified tutor. Wikiversity is another alternative. --Swift (talk) 13:39, 23 January 2009 (UTC)

## poles and zeros of transfer functionEdit

hi everyone,

I am doing a project on classical and modern design of control systems, I have got a very basic doubt as to why we always consider the degree of denominator greater that or at-most equal to the degree of numerator(i.e why is always the number of poles should be greater than or at-most be equal to zeros for any general transfer function).Please help me out to answer this question in detail.

Thanking you, yours faithfully, bhoomi