Difficulty Definition and 268 Threads

Hello PF, Can anyone tell me how hard it is for anyone to join MIT or Harvard for exemple in engineering or physics for graduate studies?

Hello I am currently a university student studying business. I am going to apply to a program in electronics and information engineering. I liked the program because it is a mix of computer science (algorithms, operating systems, software engineering and computer architecture modules) , IT...

Hello, I have to solve the following integral in Mathematica but although I don't get any mistakes the value I get is <10^-700 which can't be right! For the following values b=0.052868 c=0.998047 g=0.00762712 s=0.902416 I have to solve the following: Fx =...

I am having a hard time understanding vector transformations. I know that vectors must transform a certain way and that dual vectors (or covectors) transform the "opposite" way. What is strange to me is that the basis vectors transform like dual vectors and the basis dual vectors transform like...

Hi, I'd like to ask you if you could write a list of QFT books in order of increasing difficulty. Thanks!

Hi friends , I am an electrical engineering student , interested in applying M.S in physics program in Europe . So i have started preparing for this , when i searched the web how to study for PGRE , most effective and common suggestion is go through the recommended books for each subject and...

I know for discrete random variables Σ P(x).x = <x> Translating for continuous random variables I'm also aware of the result ∫ P(x).x dx In my lecture notes ( I more or less transcribed from what the lecturer said ): ∫ P(x).x^2 dx = <x^2> , should it not be ∫ P(x^2).x^2 dx = <x^2>? Does...

Homework Statement The displacement of a machine is given by the simple harmonic motion as x(t) = 5cos(30t)+4sin(30t). Find the amplitude of motion, and the amplitude of the velocity. Homework Equations x''(t) = -4500cos(30t)-3600sin(30t) The Attempt at a Solution [/B] I should note that...

Well known it is that the fundamental mechanics and the fundamental E&M courses of Physics for the science and engineering students are very difficult. Then the next course of this series, "Modern Physics", may seem so much less stressful, and at least a bit or more easier. Is this common? Is...

Homework Statement Given: |r|=√(x^2+y^2+z^2) r=xi+yj+zk (i)Find the partial derivative with respect to x of |r|. (ii) Find the Laplacian of |r|. Homework EquationsThe Attempt at a Solution For (i) I got x/|r| but then for (ii) I got 2/r which I don't think is correct

Given the following matrix: 2 3 0 3 2 4 0 4 2 I'm having a difficult time working out the characteristic polynomial. I used the shortcut that I saw on YT, where it is (I am using x instead of lambda) X^3 - (trace) X^2 + (A11+A22+A33) X - DET(A) I got the following: trace is just 2+2+2 = 6...

Homework Statement An Indy 500 race car's velocity increases from 4m/s to 36m/s over a 4 second time interval. What is its acceleration? 4m/s is the initial velocity, 36 m/s is the final velocity, and time is 4 seconds. Homework Equations final velocity = initial velocity + (acceleration x...

I am an advanced undergraduate student, and I still remember the days when I could open my mathematics textbooks, read through a few sample problems, and then blaze my way through the exercises with little or no help. Come university, and my freshman year, and things changed dramatically. I...

Homework Statement Automobile accidents occur in the United States over a 72 hour holiday period like events in a Poisson process with parameter lambda=10/hr. V is the time until the 10th accident a) what is expected value of V or E[V] and standard deviation? b) What is the probability that V...

Homework Statement The differential equation is xy'-2y= x3ex Check the solution y=x2 ex Homework Equations Just plug in The Attempt at a Solution y' = x2ex + 2xex Having problem solving for x.

< Mentor Note -- thread moved to HH from the technical math forums, so no HH Template is shown > Hi, I'm having difficulty solving the following quadratic equation x^2-(660/x-5)-91=0. The fact that the middle term has an x-5 rather than just an x that is throwing me Can anyone please help...

Hello all. I plan on appearing for the SAT / ACT soon (I'm still sort of on the fence between the two), and I've heard that the SAT English difficulty level is absolutely brutal. This is tipping the scales in favor of ACT, but then I've also heard that scoring in ACT writing can prove to be very...

Homework Statement I understand how to solve for stationary points, and then take the second derivative and input the values of x to determine the nature of the stationary points, if x > 0 then the stationary point is a minimum and if x < 0 then the stationary point is a maximum. What I am...

Hi guys, I have completed my first year engineering courses and about to start my second year. I enrolled for computer engineering but have decided to change to either electrical or electronic engineering. So my main question is which is more harder between the two ? I know the main differences...

I'm starting a physics major this year and I'm currently enrolled in foundation physics (algebra, vector based). However, during second semester I'll be doing doing a regular physics unit which is based around technology. The main topics are Electromagnetism (LOTS and LOTS of circuits work...

As i understand, the induced current in a wire equals -d(∫∫B⋅dS)/dt What is S? I know it has to be an open surface for the flux integral to be non-zero, but over what surface do i do the integral?

Before I get blasted by anyone, I just wanted to say that I'm asking this as a matter of curiosity and am in no way suggesting that some people/academic subjects are "better" or "worse" than others. It's strictly an intellectual question for me with no personal meaning or any other type of...

We have this stationary metric, $$ds^2 = e^{2U}(dt+\omega_idx^i)^2 -e^{-2U}dx^2$$ The book wrote down the spin connections of this: $$ \omega^{0i}=\partial_ie^{U}e^0 +e^{3U}\partial_{[_i\omega _k]}e^k $$ and $$ \omega^{ij}= e^{3U}(\partial_{[_i\omega _j]}e^0-\partial_{[_ie^{-2U}\delta_j]k} )$$...

Like I was reading Stephen Hawking and while I found quantum physics interesting, I had trouble truly understand it. I mean I know it's the study of very small particles and stuff like you cannot predict where an electron is if the more you know its velocity but I had trouble understand the why...

http://i.imgur.com/GP6QorG.jpg I don't follow the integration in it. I'm assuming Fx(x,0) and Fy(1,y) are the partial derivatives of F with respect to x and y, respectively, but given that, I can't seem to get my head around the result where the partial with respect to x is Fx = (x, 0) instead...

The physics textbook I'm working with doesn't seem to give me the required background for working with and understanding SI and derived units. Here is an example of something i am struggling with: In studying fluid resistance, the book starts by displaying 2 equations. 1 is for fluid...

Homework Statement How to evaluate the anti-derivative of [x+(7x^2)]^(1/3) ? 2. The attempt at a solution I've attempted to do so via standard integration techniques , i.e. substitution and integration by parts , but the problem simply becomes increasingly complicated . I've even tried...

Hello everybody, I'm studying classical electrodynamics and I'm having a difficulty grasping the concept of EMF. I'll try to explain what causes my confusion. Say I've got a conducting loop, an electrical wire, with some resistance R which contracts (or expands) with time. Let's put that loop...

Homework Statement I was reading in a book that, " For any function f(x) whose functional form changes from f(x) to f'(x), we can write \bar{\delta}f(x) = f'(x) - f(x) = {f'(x') - f(x)} - {f'(x') - f'(x)} =...

Hi all, I think I understand the concept of doping a group IV semiconductor material with a group V atom which has one extra valence electron to "donate" to the conduction band, or doping with a group III atom with one too few electrons which will "accept" an electron from the lattice and...

I'm having difficulty deriving a quadratic from the info in this question: A train usually covers a journey of 240 km at a steady speed of \(v \text{ kmh}^{-1}\). One day, due to adverse weather conditions, it reduces its speed by 40 \text{kmh}^{-1}\) and the journey takes an hour longer...

I'm a high-school graduate, on my way to college this September. I have this problem. I like mathematics and physics a lot, and, at least up to high-school level I've been getting good grades in it (I won the Cambridge Outstanding Learner's Award for topping A-Level Physics in my region). In...

I'm not sure if this is off-topic for this section of the forum but I wasn't sure where else to post it. I'm substantially behind compared to other physics majors at the moment (3rd year student with enough credits to be considered mid 4th year student) so i wanted to pick up the pace. I like...

1. The problem For sake of format I attached the a screenshot of the course material I'm having difficulty wrapping my walnut around. Which is how: Total Displacement = Area of Triangle + Area of Rectangle or Δvector d = Atriangle + ARectangle or Δvector d = 1/2 (V2-V1)Δt +V1*Δt...

Dear friends I have tried to electroetch 1050 aluminum alloy by 5ml phosphoric acid + 95ml H2o under 1 to 10 volts. However, it was a complete failure even after etching for 6 min. Please help me if you know how to overcome this problem. Thank you very much Best regards

Okay, I understand this is a highly trivial problem, yet for some reason, it is bestowing much difficulty upon me. If a diffraction grating has 500 slits/mm, what is the spacing between each slit? Evidently the spacing between each slit is given by the inverse of that ratio. I am having...

Hey, I'm really struggling with this 'show that' question regarding the secant method, I just keep going in circles and I think I may be heading in completely in the wrong direction because I'm not getting anywhere. Homework Statement We're given that, if x* is the zero of f then (we...

Homework Statement Let a,b,c,d be real number that satisfy the property that a + b = c + d and a^2 + b^2 = c^2 + d^2 . Show that a^n + b^n = c^n + d^n for any n , a natural number ( with n > 0 ) . Homework Equations x^n - y^n = (x-y)(x^{n-1} + x^{n-2}y + x^{n-3}y^2 + ... +...

if a,b,c are in continued proportion .prove that (a+b+c)^2/(a^2 + b^2 +c^2 )=(a+b+c)/(a-b+c)

Is there only one point where the line connecting the two skew lines is perpendicular to them both? And is that point always always always the place of closest approach? Thank You

Hi all, I am trying to find the slope of a T-stub joint at the bolt in order to find the bending stress of the bolt. I have drawn 1/2 of the T-stub as a beam. The beam analysis requires (for physicality) that the slope at each side of the beam to be zero. There is an applied load, a bolt...

Hi all I am struggling to create a response surface for some data I collected. I have been asked to create a response surface to get a better understanding of how the two inputs of interests affect the output. I threw together a multiple linear regreession model since it was simple but my...

Hi, I am struggling trying to find the (equation of the) pdf of the sum of (what I believe to be) two non-central chi-squared random variables. The formula given on wikipedia (http://en.wikipedia.org/wiki/Noncentral_chi-squared_distribution) shows that the random variable associated with...

Hello, I've come to the point where I realize: I'm supposed to teach. I've tutored for years, taught small groups, etc. Also, I want the summer to pursue my other interests. I don't want to do research or anything; just teach. I was just curious as to how competitive these jobs are...

Homework Statement Given that lim f(x) = 4 x → 2 lim g(x) = -2 x → 2 lim h(x) = 0 x → 2 find the limits that exist for the problems below. If the limits do not exist, explain why.c) lim √f(x) x → 2 e) lim (g(x)/h(x)) x → 2 Homework Equations lim √f(x) x → a = √(lim f(x)) x → a and...

I know how the very basics but then I get given a question like this. ##\sqrt{9-3x}## and I think I can divide both by 3. ##3\sqrt{3-x}## and so ##x=3## Then I get ##\sqrt{4x+12}## and again I can take 4 from each ##4\sqrt{x+3}## and so ##x=-3## Is this the correct way to be solving these...

I'm having some difficulty compiling a test project within Visual Studio 2010. I'm trying to test the Seldon package, but keep getting errors during build. Specific errors I'm getting include (and vary between): // Headers from CLAPACK, downloaded at http://www.netlib.org/clapack/. //...

Let ##G## be a set equipped with a binary associative operation ##\cdot##. In both of the following situations, we have a group: 1) ##G## is not empty, and for all ##a,b\in G##, there exists an ##x,y\in G## such that ##bx=a## and ##yb=a##. 2) There exists a special element ##e\in G##...

Hi, I've studied mathematics at high school and I will start university next year. I'm worried about my mathematical knowledge in general. There are many "gaps" which lead to confusion. To give you some examples: 1) I've difficulty understanding why, for instance, 5 - (-2) = 5 + 2. The only...

My university is offering a course called "Stochastic Process". The only prerequisites to this course according to my university is a course in Probability which uses the book by Rosen. I've read elsewhere that the course actually requires more of analysis (functional analysis and measure...