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Unanswered Cries for Help!      Total So Far: 43
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GR8677 #39
2017-04-08 00:55:51
I\'m confused. Choice (E) resembles the function y = \\frac{1}{x^2} which has positive concavity, not negative like the graph shows.
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GR8677 #99
2016-03-12 23:07:10
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GR8677 #63
2015-12-19 21:09:12
I am really very happy after getting the unlimited roblox robux generator which allowed me to acquire the whole world in playing roblox with much ease after following the given link.Through it http://www.robloxfreerobuxgenerator.com/ i was able to access the whole world in roblox and enjoyed every little bit of it.
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GR8677 #98
2015-09-04 09:22:09
I tried to solve this problem in an alternative way, which is less simple and convenient than the official solution on the site, but unfortunately failed to get the correct answer. I can\'t find my mistake and I am quite baffled. I shall deeply appreciate if someone would like to offer me help soon!\r\n\r\nMy solution is to integrate the intensity of electric field E at the point P first, and then integrate the electric potential at the same point. \r\n\r\nAssume the linear electric density \\lambda,\r\nQ=\\lambdaL, dQ=\\lambdadx,\r\n\r\ndE=\\frac{kdQ}{(l+x)^2} =\\frac{k \\lambda}{(l+x)^2}dx, \r\n\r\nE=\\int_0^l \\frac{k\\lambda}{(l+x)^2}dx,\r\n\r\nApplying the substitution method, set u=x+l, du=dx, so\r\nE=k\\lambda\\int_l^{2l}\\mathrm{u}^{-2}\\,\\mathrm{d}u=k\\lambda[\\frac{-1}{u}]=\\frac{kQ}{2l^2}.\r\n\r\nHence, V=\\int_l^\\infty\\vec{E}\\mathrm{d}\\vec{l}=\\int_l^\\infty\\frac{kQ}{2l^2}\\mathrm{d}l=\\frac{kQ}{2}[\\frac{-1}{l}]=\\frac{kQ}{2l}.\r\n\r\nSo my answer is the choice B. \r\n\r\nCan someone tell me where I did wrong?
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GR8677 #98
2015-09-04 08:42:18
I tried to solve this problem in an alternative way, which is less simple and convenient than the official solution on the site, but unfortunately failed to get the correct answer. I can\'t find my mistake and I am quite baffled. I shall deeply appreciate if someone would like to offer me help soon!\r\n\r\nMy solution is to integrate the intensity of electric field E at the point P first, and then integrate the electric potential at the same point. \r\n\r\nAssume the linear electric density \\lambda,\r\nQ=\\lambdaL, dQ=\\lambdadx,\r\ndE=\\frac{kdQ}{(l+x)^2}\r\n =\\frac{k \\lambda}{(l+x)^2}dx, \r\nE=\\int_0^l \\frac{k\\lambda}{(l+x)^2}dx,\r\nApplying the substitution method, set u=x+l, du=dx, so\r\nE=k\\lambda\\int_l^{2l}\\mathrm{u}^{-2}\\,\\mathrm{d}u=k\\lambda[\\frac{-1}{u}]=\\frac{kQ}{2l^2}.\r\n\r\nHence V=\\int_l^\\infty\\vec{E}\\mathrm{d}\\vec{l}\r\n =\\frac{kQ}{2l^2}\\int_l^\\infty\\mathrm{d}x.\r\nFinally, there comes out infinity of the electric potential. \r\n\r\nCan someone tell me where I did wrong? \r\n
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GR8677 #77
2015-08-12 08:58:27
WOW! My solution looked fine in the preview. Sorry, for that jumbled mess of latex jargon... help?
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GR8677 #58
2015-03-23 12:27:14
I'm a little confused about notation in chemistry. In Quantum Mechanics, the notation of (2s+1)^L_(j) is used where L is a place holder for the total angular momentum quantum number (l=0 ->S, l=1->P, l=2 ->D, etc). How does 2s+1 relate to the proton number, in this case Z=11. The solution says to sum up the superscripts to see which add up to 11 but why?
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GR8677 #52
2013-10-18 11:28:05
I tried this method and it gave me an entirely wrong answer (a^3/12). I assumed that we would want the volume of the shape made by the primitive vectors, which would be a small tetrahedron. If someone could explain a way to understand this problem geometrically (similar to what Karsten is trying to do), that'd be really helpful. I understand the shortcut way of dividing the total volume by the number of lattice points, but I'm really craving a geometric argument that's more intuitive.
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GR8677 #17
2013-10-14 17:28:53
The shape you get is also very dependant on the phase difference; see: http://en.wikipedia.org/wiki/Lissajous_curve Anyone know how to quickly get the answer?
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GR8677 #93
2013-10-12 09:40:21
If we take E=0, wouldn't the particle have no period? The only choice that satisfies this is (C) but (C) is incorrect.
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GR8677 #18
2013-08-15 18:08:12
This should be classified as HELP!, haha
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GR8677 #61
2012-10-11 01:04:05
I have to solve a problem by using Coulumn' law given rho=rho not (1-r/R) and find Q from given expression.
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GR8677 #27
2012-09-18 07:17:56
Can anyone help me with an study reference about these graph stuff?
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GR8677 #16
2011-11-07 00:38:10
question: how have you come to approximate the variance as 5?
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GR8677 #9
2011-10-27 08:19:34
I'm confused on where the cosine and sine equation above came from. Was this an trigonometry identity? What does S stand for?
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GR8677 #62
2011-07-28 04:44:09
I, too, don't see how the capacitors are in parallel. The problem statement says nothing about this, and we could equally likely consider them in series...So what is the point here ?
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GR8677 #62
2011-07-28 04:40:12
That figure does not exist anymore, could you please reupload it ?
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GR8677 #10
2011-02-28 16:53:23
Why is the direction of the -q and -2q equal to \hat{x} and not -\hat{x}? I understand that the forces add up from drawing out the Forces... but mathematically my magnitude sum is not as I expected it to be since i used -\hat{x} as the direction of the force on q for -q and -2q.
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GR8677 #32
2010-11-02 01:28:14
isn't A the center of mass?
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GR8677 #39
2010-10-08 16:31:44
More detailed explanation on finding slope of log-log plot: http://en.wikipedia.org/wiki/Logarithmic_scale#Slope_of_a_log-log_plot
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GR8677 #67
2010-04-09 19:57:04
Just think of it as the superposition of two waves one that is polarized and one that is partly polarized add these together (think a circle and a ellipse) and you will get the combined wave.
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GR8677 #41
2010-03-29 10:27:51
I should have said A instead of Z , since neutrons have spin of one-half as well.
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GR8677 #41
2010-03-27 13:14:14
Some texts include the spin of an odd nucleon in the total Russell-Saunders coupling sum of spins. I don't know why it is sometimes included and sometimes not. Perhaps that is why ETS has designated the state as S=1, because they are including the spin of the proton. The problem with this method is that all atoms would have a total integer spin, zero for even Z, and one for odd Z. Does anyone know when to include the odd nucleon and when not to in the total angular momentum? It seems that it should always be included. I don't think that electronic shielding in larger atoms would change the total angular momentum.
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GR8677 #71
2010-02-18 08:22:12
I like your idea about using common sense, and it works, however, in this case the answers B and C are very close, in the moment of the test, under pressure is very hard try to deicide about one of them. There is an alternative way to do some basic calculation to give the right answer, beteween B and C?
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GR8677 #65
2009-10-31 14:07:08
What is the result of dimensional analysis for Coulombs or Amps?
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GR8677 #99
2009-04-01 18:35:24
Please excuse my ignorance. How did you get this formula for E_{f}?
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GR8677 #67
2008-10-28 11:10:05
So the absolute temperature is when T \rightarrow \infty? Is that what they mean by absolute temperature?
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GR8677 #47
2008-10-27 09:47:20
kevglynn: Doesn't "a sealed and thermally insulated container" mean adiabatic ?
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GR8677 #92
2008-10-14 10:56:46
Same question on choice (A)...the subject GRE test is coming soon, anyone care to explain?
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GR8677 #22
2008-09-27 23:01:00
I take issue with this answer! This is the way I did it. 1. Given Rmin and Rmax you can sum them and divide in two to determine the semi-major axis, a. Thus choice E is eliminated 2. Given Rmin and the semi-major axis you just found, you can compute the eccentricity: Rmin=a(1-e) where a is the semi-major axis and e is the eccentricity 3. Given Vperi and Rmin you can calculate the mass of the planet: Vperi = sqrt{(GM(1+e))/Rmin} Thus choice B is eliminated 4. Similarly, since Rmax was also measured, you can now find the minimum velocity, which will occur at apastron: Vap= sqrt{(GM(1-e))/Rmax Thus choice C is eliminated Now we are left with the mass of the moon or the period of the orbit. Kepler's law is *actually* P^2= (4pi^2)a^3/(G(M+m)) Note the denominator contains the *sum* of the masses! So we truly have one equation left with two unknowns. You *cannot* calculate the *exact* period from here. You can only make an approximation where you neglect the mass of the moon, but that seems like a self-fulfilling prophecy or circular reasoning to me. Saying "a very small moon" is very subjective. What if the planet, too, is very small? They don't state the ratio of the planet to the moon, or mention that it is negligible in size compared to the planet. So how can we really use Kepler's law in approximate form in this case?
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GR8677 #82
2008-09-25 03:46:39
I don't understand. Why should we consider only reflections at the top and the bottom of the air gap? Why not the reflections at the top of the upper glass plat and the second glass plate?
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GR8677 #94
2008-09-21 17:12:38
Wait, how are we in the clear??????? If gamma really is 5/4 then beta should be 3/5. Beta is clearly 3/4 = 0.75 So how is it a valid transformation?
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GR8677 #4
2008-08-18 01:43:44
I believe that choice E has the same dimensions as A&B.
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GR8677 #4
2008-08-18 00:58:43
I believe that choice E has the same dimensions as A&B.
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GR8677 #76
2008-08-01 13:01:11
Sorry, this should have been categorized under HELP :D
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GR8677 #78
2007-10-21 21:28:08
I'm not really seeing why the tangential velocity of the two masses together is equal to the sum of their original linear velocities. Why can they be added this way?
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GR8677 #16
2006-11-30 21:43:30
if you claim that \overline{x}=2 is the average and \sigma=\sqrt{\overline{x}} is the standard deviation, then how do you go from there to get that \sigma/\overline{x}=\sqrt{2C}/2C is the answer? I'm confused as to how the C's get in there
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GR8677 #7
2006-11-01 10:44:16
Can you explain in greater detail? I can solve it, but I run into some messy algebra with quadratic equations. Can you explain how you so elegantly obtained these values?
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GR8677 #41
2006-10-29 21:40:11
Can anyone direct me to a good explanation of the full spetroscopic notation and how it relates to the selection rules?
More specifically, what part of this notation denotes m, the magnetic quantum number?
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GR8677 #34
2006-10-27 15:15:32
hey
i cant get enough practice problems for quant. i have got schaum seeries but it has only derivations any one has any material plz i want it
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GR8677 #100
2006-10-27 14:07:24
hey watz up to begin iam a BE undergrad shifting to engineering physics.
any ways i just wanna know from where do i study error analysis. if any one has the notes on the comp plz mail them to me.
also if any one has practice problems (except for the four papers and two small other ones) specially for phy gre plz i want the soft copy.
bye, best of luck to everyone
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GR8677 #64
2006-10-19 13:49:09
What's this about a capacitor and an inductor? Problem 64 from 86 exams says "An alternating current electrical generator has a fixed internal impedance..." ?
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GR8677 #47
2005-11-10 21:33:24
Why is C the more correct answer than A? Your last comment in the introduction makes this seem confusing.
 
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