Confused Definition and 1000 Threads

Hi, I have this problem that is solved, but I don't understand the theory behind it. It says: Which of the following sets, with the natural definitions of addition and scalar multiplication, form real vector spaces? A) The set of all differentiable functions f:(0,1)\rightarrow\Re such that...

when i was 14 and my mom walked in my bedroom and turned the light on to wake me for school she couldn't wake me up and my eyes were rolling in back of my head she tried walking me around but my body was limp she called ambulance but i was fine by the time they got there they took me to the...

Hi. I am reviewing for an exam, and this is a topic that I did not go through very thoroughly. I understand how to calculate the derivative of an inverse function when I am given a point, as I simply use the equation (1/f((f^-1))'. So if I am given the equation y=x^3, for example, and am asked...

Hi, been reading about GR and am quite confused about the new definition of vectors. My main problem with this is that the text uses partial derivatives as the vector basis, I understand this is related to directional derivatives but cannot see the direct mathematical relation. Secondly, how...

Hi, I'm looking into the control of a PMSM (permanent magnetics synchronous motor) motors using H-briges and PWM (puls width modulation). I'v seen motor controllers that use a PID controller for speed regulation. The output of the PID controls the PMW. This makes sense to me because the PMW...

Now let's say I have the metric for some curved two surface ds^2=G(u,v)du^2+P(u,v)dv^2 ( the G and P functions being the 00 and 11 components, assuming the metric is diagonal) Now my question is, since the metric defines the scalar product of two vectors, let's say (1,0) and (0,1), for...

I (and probably everyone) like to learn from books that describe the reasoning/philosophy behind the equations as much as possible, instead of "pluging this in and getting that" or even just dishing out "clearlys". There's a footnote to the word "clearly" in some online LaTex tutorial...

A and B or C Does that even makes sense as a statement? I thought logical operators are binary. Obviously, the "or" links to C but what is on the other side? A or B? i mean 1+2-3=0 makes sense since (1+2)-3=3-3=0=1-1=1+(2-3) But [(A and B) or C]=(AorC)and(BorC) [ A and (...

Maybe this should belong in the logic section. But since this is C++, ill put it here. bool isLeapYear( int y) { return y%4==0 && y % 100 !=0 || y% 400==0 ; } They said it returns when y is divisible by 4 but not by 100 unless it is also divisible by 400. This is a bit...

So as I have read in Schutzs book on GR, and I'm finding his section on tensors and one forms very confusing. Schutz describes gradients of functions as a one form, I cannot quite grasp why. In calculus I was taught that the gradient was a vector pointing in the direction of the fastest...

I have to preface my questions by saying that I have only a little better than a high school understanding of physics; as such I humbly ask that any answers be termed in a way that I'll be able to understand them. I've read that the universe has a radius of ~ 46 billion light years. And we...

So from looking at a lot of universities' graduate programs for science Masters and PhD's (physics, engineering, materials science, chemistry, molecular biology, etc), a lot seem to offer pretty good stipends (in the $20,000 - $30,000 range) if you enter a research-based program and do research...

Homework Statement I need to approximate the number 14.45 to nearest integer. Homework Equations The Attempt at a Solution If I remember correctly, to approximate a decimal up to say 2nd decimal place, I look at the third digit and if this is greater than or equal to 5, then I...

Hi guys, I just started reading an introductory book on analysis. I'm up to the part where they talk about functions now, and I'm getting lost. The theorem that I'm having trouble envisioning is: Let f: D-> R and let c be an accumulation point of D. Then limx->cf(x)=L iff for each...

Hi, so this isn't a question, it's just an example that they've given, but I don't understand the explanation given. You have : y = x^2 - 4 x = y^2 - 4 y^2 = x + 4 y = ± sqrt(x+4) I don't get why there is a ± symbol there. My book says that it's necessary because there are two...

So I know these equations 1/f = 1/p + 1/i m = -i/p f: focal length p: object distance from mirror i: image distance from mirror m: magnification Let's say that I have an object in front of a concave or convex mirror with the same |f|. p is much larger than the radius of curvature...

Hello, please take a look at the image below: http://tinyurl.com/cnz2sut I am confused as to how that square root transformed into 3/2 power... Isn't it suppose to be 1/2 power if it's a square root? Thanks

I'm doing AQA Physics A unit 5 next Monday, and I've been doing some past papers but I'm not sure about how to answer questions on the energy released in nuclear reactions. The mark schemes say that the energy released is equal to the change of binding energy per nucleon but I thought that the...

Homework Statement α=2e3∏i/4 find α11 in cartesian form. Homework Equations The Attempt at a Solution It's been a while since I've done these but from what remember you add 2kpi to get exp in the range of -∏,∏. so if I let k=15 I get e3∏i/4 but the sltn says it...

I am sick of searching and being confused more and more specially about lenz law... THere are many demonstrations and many law.. Can someone list atleast the most important one...

I'm confused when i consider about this picture in my head. ... imagine that there is a ''closed-box'' on the floor. And ball A is in this closed-box. Pressure acted on the box = Patm. I'm wondering, how much pressure act on ball A ? With my sense, i think it is Patm. ... but i can't...

So I started researching about aerodynamics and found that the most natural aerodynamic thing is a teardrop, it has a very low coefficient of drag so cars had been made to also have aerodynamics like a teardrop but looked horrible so no one bought them but engineers now decided to make a more...

Homework Statement a 2 kg block rests on a horizontal frictionless surface, and is initially at rest. a 1 kg block rests on top of the 2kg and initially moving at v=3m/s (to the right). the coefficients of friction between he two blocks are MUs=.2 and MUk=.1 . A force is applied to the top...

When I first started learning about GR, I understood that a vacuum solution is one where the Einstein tensor vanishes, for the simple reason that the stress-energy tensor, T, vanishes. I have since read many times that the Ricci tensor vanishes for a vacuum solution. I am confused because to...

Hello people! I am having a bit trouble with verifying my result when i compute the eigenvectors for the following matrix: A=[[3,4],[3,2]] I know for sure that the eigenvalues is respectively -1 and 6, so i start finding a solution for the following null spaces: 1)...

Hi I'm taking a multimedia systems course and I'm preparing for my exam on tuesday. I'm trying to get my head around LPC compression on a general level, but I'm having trouble with what is going on with the linear predictive filter part. This is my understanding so far: LPC works by...

Confused about the formation of "Stuff" in an Isotropic-ish Universe First let me state my current understanding so that I can be corrected if not on the right page-- Given "zooming out" far enough, our universe is rather homogenous/isotropic, but not perfectly so. If this is correct, I must...

So we're converting these currents from phasor to time domain with ω=4. I understand I1, but not how the lecturer got I2, is this an error with the notes? We have these phasors: Which are converted to this time domain (respectively): Any help is much appreciated.

Hey guys, stupid question probably, but I somehow don't get it. I'm just reading an article about dark matter in elliptical galaxies. They mention at a certain point that while for the detection of DM in spiral galaxies we measure the rotational velocity of its stars around the center, for...

I know what E-Z isomerism is, but I'm confused about Q9), couldn't the answer just be all of them? FOr 10, I know its but- since there are 4 carbons in the chain but how do I know which of the options are wrong? Thanks

Homework Statement Suppose 5 cards are dealt at random from a well shuffled, 52 card deck. The hand can be thought of as a random sample size 5 from 52, with no replacement. What is: (a) P (4 aces) (b) P (3 aces and 2 kings) (c) P (4 of a kind) Homework Equations I know the...

alright, well here's my story (sorry for the long read, heads up now lol :P) in high school, i did absolutely no work at all. i pursued all the sciences however and did fairly well in biology and chemistry as well as math (advanced functions and calculus). thing is, never had an interest in...

Hello, and greetings! I am a senior in High School, but had the revelation this year that I want a career (and education) in science. I've narrowed down my interests as best I can, but my area of interest is still fairly broad. I'm aware that this post includes career advice, but it is tied...

I'm working on a project that required me to go through the literature to find some information on Compton and Rayleigh scattering. I came across a key expression, part of it which read: max{ f(x,Z), g(x,Z) } if Z > 10 and f(x,Z) < 2 where f(x,Z) and g(x,Z) are known functions. The...

Homework Statement This was a question on my test. I had to choose the direction of the acceleration vector for each position. I was wondering if I chose the correct answers. Homework Equations a = gsinθ ƩF_{y} = N_{1S}( normal force) - W_{1E} ( weight force) The Attempt at a...

I'm so confused lately :( I want to get into a field where we integrate chips with the brain, or try to make neurons interact with engineering devices. Problem is I don't know what field fits best. Which would you recommend me, based on experience? Medical engineering seems like the ideal...

Ok I'm really trying to understand inertial and non-inertial reference frames, my understanding is as follows: A rest observer on the earth, the observer will be stationary relative to the earth.. Now as I understand it an inertial reference frame is one of which 2 coordinate systems are both...

I=mr^2 I know moment of inertia depends on how for a object how far a bit of mass of that object is from the axis of rotation. i.e. farther from the axis = higher moment of inertia-= more torque is needed to cause rotation. this just doesn't make any sense for the seesaw example, on the seesaw...

Homework Statement Find the derivative of f(x): f(x)= 1/ ((ln(x)^2)) Homework Equations f(x)= ln(x) f'(x)= 1/((ln(x)) The Attempt at a Solution Dx(1/ln(x)^2) = Dx((ln(x))^-2)= -2*(ln(x)^-3) * Dx(ln(x)) = -2*(ln(x)^-3) * 1/x = -2/(x*ln(x)^3) Are these the correct...

Hi everyone! I have the following problem which I don't understand... It is already solved, but there are three questions I have regarding it. The problem says: "Let S be the set of all vectors x=(x_{1}, x_{2}) in \Re^{2} such that x_{1}=1. What is the span of S?" And here is the answer...

Homework Statement How much work must you perform to lift a 5 kg bag from the floor to the countertop, 1 meter above the floor? 2. The attempt at a solution A. You could say that any force greater than the weight of the bag would lift it up. Thus, the weight is 50 N and the force...

Hey Everyone, If you have an electron with the various energy levels: -14 eV, -30 eV, -52 eV, -80 eV. And that the electron can only move between these levels. How do I go about finding the photo energy that is emitted? Do I just subtract the various levels? Ex. 14 - 30 = -16 etc?

As you probably know, the thin-lens equation is given by: 1/s + 1/s' = 1/f where s = distance from object to lens, s' = distance from lens to image and f = focal length of lens Now, in a particular question, I needed to find s' given that s = f. From the equation, that means s' would become...

I only just started learning about special relativity in my physics class, and I have been running into a problem that none of my teachers have satisfactorily explained. Objects X and Y are moving relative to one another at some significant fraction of the speed of light, where ɣ is the...

Homework Statement I have a final coming up and I am a bit fuzzy on how to create a matrix that represents a rotation or reflection about a certain plane (in R3). Say we are given a rotation/reflection about either a plane or a line through two points T(v)=Av and we are told to find A. Do we...

I am confused a bit :confused:. I read in a paper that the following property holds, but can't find where it comes from. \mathsf{E}\left[X(\omega)X^*(\omega')\right]=2\pi\delta(\omega-\omega')S_{XX}(\omega) it says that the expected value of the Fourier transformed signal is proportional...

Hey. New here. I am a 12th science student, from India. I LOVE science. I have been dreaming of becoming a physicist since class 6. So obsessed with it..i even dreamt of Einstein once! :-p But its not a crazy obsession..i know what all sacrifices i'll have to make for it. Financial instability...

Ok; so basically, I am creating the game of Nim through gate chips (AND/OR/NOT), switches, and yea all the basics. I have pretty much completed designing and physically building the game but I have been having issues with one portion of the design -not the logic of the design.I have a regular...

Homework Statement A coil with zero resistance has its ends labeled a and b. The potential at a is higher than at b. Explain why the two following statements are consistent/correct with the situation. a) The current is increasing and is directed from a to b. b) The current is decreasing...

Homework Statement differentiate the following y= x(x+2)(x+3) Homework Equations dy/dx The Attempt at a Solution The answer I'm given is dy/dx = 2x+5 Would this not be for (x+2)(x+3) = x2 +5x +6 dy/dx = 2x +5 +0 My problem is the x at the beginning of the brackets. Please...