Confused Definition and 1000 Threads

I was hoping someone could help me understanding winding numbers For e.g. the point -i that is (0,-1) on this curve... I was trying to determine if the winding number was 2 or 3 http://img15.imageshack.us/img15/1668/11111111111111countour.jpg

Homework Statement You have 7 birds lined up to feed. Only 3 birds can feed at a time. Two of the 7 birds do not like to feed with each other. How many combinaions can be formed?Homework Equations C(n,k)=n!/k!(n-k)!The Attempt at a Solution Attempted solution C(7,3)-C(7,2)=21. That is the...

Homework Statement I'm given the member function: bool Product::is_better_than(Product b) const { if(price==0) return true; if (b.price price==0) return false; return score/price>b.score/b.price; } I'm really confused about the last line "return...

([SIZE="2"]Moderator's note: thread moved from "Linear & Abstract Algebra") problem # 12). Suppose X is a finite set with n elements. Show that the semigroup X^x has n^n elements. I'm confused. Isn't semigroup a set of functions? So when it says n elements, it actually means n functions? Also...

Homework Statement Use polar coordinates to find the volume of the solid enclosed by the hyperboloid -x^2-y^2+z^2=1 and the plane z=2. The Attempt at a Solution Solving for z of the equation of the hyperboloid I find z = Sqrt(1 + x^2 + y^2). Letting z = 2 to determine the curve of...

I know I know. This question must be uber easy in the eyes of you genius'. But the truth is - I'm taking grade 12 physics when I practically failed grade 11(well, I got 51...I wasn't trying, I swear!) so getting some of the concepts can get very confusing...and frustrating! Nonetheless, I need...

Hello, I have a question that's really bothering me. So I've been reading about projected capacitance touchscreens (the kind that's in so many cell phones, the iphone etc) and I don't understand what the physical property of my finger is that allows the screen to function. From what I've...

Hello, This is my first post in this forum.I signed to ask some sort of guidance from you people:smile: Well its like this: I always had an interest on civil engineering for many years now (structures, skyscrapers, designing), so I knew from the start which career path I would want to...

this is going to sound really dumb, but here is my questions anyways: is (u(x,t))2 the same as u2(x,t)? I say yes, but I am not sure. thanks spoony.

What is the definition of the lie algebra \mathfrak{so}(2,1)? i want to say that it is the set \{ X \in GL(3,\mathbb{R}) | X^t=-X \text{ and } \text{trace}(X)=0 \} is that true?

Hello. I signed up to get peoples opinion. See, I have no one to talk to about my situation or quantum physics, so here it goes. I am 23 and have no school experience. I am a natural at computers, but my real passion of course is quantum physics. When I learned about quantum my whole entire life...

I don't know the beginning part of the question is relevant, so I'll leave it out unless requested. At the point of: \intsin\varthetad\varthetad\phi Which is to be integrated over a sphere, when integrating from 0 to pi for \vartheta and then from 0 to 2pi for \phi, we get 4pi, which is...

Hello, I was trying to do this problem and then I looked at the solution manual and found something that confused me. I am having trouble distinguishing between centripetal and radial acceleration. According to the equation in the book a_r=-a_c, which kind of confuses me. Isn't a centripetal...

Hello, I have studied X-ray emission when an electron beam is fired at a tungsten target - But when I was presented with the graph of Intensity versus wavelength, I was confused... I saw a curve, and on it there were spikes. What are these spikes, and why are they caused? Something to...

Homework Statement Homework Equations F = Ma The Attempt at a Solution ... I wish I even knew where to start :\ I drew the freebody diagram, but I don't know how to use it.

The experiment was to measure muzzle velocity of a ball fired by a 'spring gun'. Then to use the equations of projectile motion in order to determine the projectile trajectory. During the experiment we used a variable-height platform to stop the ball mid-air (at y = 0.4 m & y = 0.1 m). Now we're...

Homework Statement A package is dropped from a helicopter moving upwards at 15 m/. If it takes 25.0s before the package hits the ground, how high above the ground was the package when it was released. Disregard air resistance. Homework Equations I used this kinematic equation...

If A \subseteq B does that mean A = B which means B = A because if A is a proper \subset of B then A does not equal B right. I am wrong right?

I recently saw a YouTube video of a 2009 lecture by Lawrence Krauss. He says that we now know unambiguously that the universe (and I just mean the universe that we can see, back to the big bang, not the multiverse or the foam or any of that) is flat. But it seems to me that a flat universe with...

Can anyone help me. I am very confused about the chemical potential. In the following equation dU = TdS - pdV + u dN, where u is the chemical potential it seems to me that if you add particles to a system you are increasing the energy of that system, i.e. the chemical potential is...

I went to wikipedia to look up decoupling and ended up getting a pretty crappy result "In physical cosmology, the term decoupling is often used for the moment during recombination when the rate of Compton scattering became slower than the expansion of the universe. At that moment, photons...

We're working on the parity operator in my second semester quantum mechanics class and there is one point I am confused about, either in the definition of degeneracy or in the parity operator itself. We talked about a theorem whereby the parity operator and the Hamiltonian cannot share...

Homework Statement In Fig. 28-5a calculate the potential difference across R2, assuming = 14 V, R1 = 6.0 , R2 = 3.0 , and R3 = 2.0. (image isn't working online, but it's a simple circuit- all the resistors are in series) Homework Equations V = IR The Attempt at a Solution Req...

Homework Statement a 4.22g mixture of CaCl2 and NaCl was dissolved, and then treated to precipitate all of the Ca as CaCO3, which was then heated to drive off CO2, leaving a sample of pure CaO which was found to weigh 0.969g. What percentage of the original mixture was CaCl[/SUB]2[/SUB]? I...

why the equilibrium constant only depending on temperature but not concentration and partial pressure ? Since K= [product]/[reactants], why the value of K remain the same as [product]or [reactant] increase ?

Hi Guys, I really wish that you help me in my problems, cause I can't take the mental torture anymore. I just graduated with a degree in Electrical Engineering. The job market doesn't look good and the crisis took its toll on all of us recent graduates "lucky us". To be honest, I...

Say we have two non-commutative operator A, B. Now I have prepared identical systems in eigenstate of A, then I measure the observable of A, and then B immediately after. Then I must have delta A=0, so no matter what delta B is, the product is 0, seems to violate the uncertainty relation...

Homework Statement Our tutor has given us an equation to think about: Homework Equations integral of sin 1/x I'm pretty sure it's insoluble but how would I go about showing it is? The Attempt at a Solution No idea where to start any advice, tried by parts but it ends up in a mess? Not...

I have recently finished "Gravity from the Ground Up: An Introductory Guide to Gravity and General Relativity". Great book, but I am confused about the behavior of time at the event horizon of a black hole. I spent some time looking at existing threads on this site, but was unable to find...

I hope someone can explain this to me: In multiple textbooks I've seen it said that a single particle wave function (no spin) transforms as a Lorentz scalar. I.e. if we have a Lorentz transformation from an old frame to a new frame \overline{x}=\Lambda x (x is short for (t,x,y,z)) then...

Homework Statement If x = yz and y = 2sin(y+z), find dx/dy and d^2x/dy^2 Homework Equations The Attempt at a Solution I am beyond confused at how to even start this one, the problem is not like any of the examples in my book. I know x = ydz + zdy but don't know how to deal...

It seems to be an easy question but for some reason I can't figure it out. Homework Statement If the 10 lb block A slides down the plane with a constant velocity when θ = 30°, determine the acceleration of the block when θ = 45°. Homework Equations F = ma The Attempt at a...

Hi everyone, I have a question maybe one of you can help me out. I have been working on a solid state tesla coil made with mosfets and a sg3524 PWM chip, I have got it working and am in the process of adding a current limiter to it (Mosfets can get expensive). The current limiter works with a...

1. There is a pendulum of Length 2.1m. Its bob has speed Vo when the cord makes the angle 48' with the vertical. a) what is the speed of bob in lowest posotioin if Vo=8m/s? What is the least value Vo could have is pendulum is to swing down and then up to: b) a horizontal position c) a...

I'm thinking of building a small vertical-axis wind turbine as a project over school vacation. By small I mean maybe three feet across and three or four feet high. I'm trying to come up with the best design. This type of turbine is good at generating torque, not RPM's, so I want to try to...

Hi, I am trying to calculate as best but simply as i can the (approx) thrust from a propeller.. and my research shows i have to calculate: prop velocity(pv) = pitch * rpm with pv i can then use Bernoulli's equation to calulate the pressure and multiply it by the propeller surface area...

This is my first post in this forum. First and foremost, big thanks to anyone who takes time out to help me with this. I work for a fire protection company; one thing i service is fire hydrants. I recently discovered this and do not understand why this is happening: A hydrant contains...

I'm confused! Gravity is the weakest force...right. How is it possible to hypothesize that a black hole scenario of gravitation being stong enough that nothing else can escape?

Guys I know how to solve the simple ones but this one has complex roots I have to find the zero input response (D-1)(D2+1)y(t)=(D2+2)f(t) y(0)=4 y'(0)=3 y''(0)=3 D2= D square. Y' = first derivative Y''= secondI know the roots are +1, j and -j But I don't know how to solve or...

Ever since I took a "high-level" math class (grad level topology), I have been baffled. This baffling has been further confounded by a couple of math-methods courses in which the professor was a highly gifted and recognized mathematical physicist, and so very careful (and picky) about the...

Hello everyone, Quick questions. What do they mean by different polarities in anti parallel DNA strands. Are they referring to some chemical polarity or simply the fact they run in opposite directions. I'm confused with DNA replication. DNA polymerase can only synthesize DNA in 5' to 3'...

Homework Statement http://img692.imageshack.us/img692/6661/36979008.jpg Homework Equations The Attempt at a Solution whats wrong with it? I am 100% sure and i can explain each one! the first one equals 3 right? second one should be true because 0/0 can be any number.. (thats...

Rotation question. Plz please please help. I am so confused Homework Statement Two masses m1 and m2 are connected by light cables to the perimeters of two cylinders of radii r1 and r2 respectively, as shown in the diagram above. The cylinders are rigidly connected to each other but are...

Here is the problem. If you roll 5 six-sided dice at the same time, what is the probability that the sum of the roll is 20? This is the solution that someone did. The problem can be viewed as distributing 20 identical objects into 5 containers so that each has between 1 and 6 objects...

A box contains 5 white balls, 3 red balls and 2 green balls. The balls are taken from box. With replacement and taking a total of 3 balls, P(all balls have different colour)=(5/10)x(3/10)x(2/10) x 3! =0.18 This answer is the same as at the back of the book. My explanation is that a white, red...

this is a problem confusing me, which is in the book named Principles of Quantum Mechanics by R. Shankar. This problem is not about quantum mechanics, but just in the chapter of Review of Classical Mechanics. (The ******** is just to avoid to be deleted). The problem is in the attachment...

For some reason I've thought about the following case : A uniformly non conductor charged disk is rotating with an angular velocity \vec \omega. If I see it in front of me I'd observe a magnetic field since moving charges produce a current which produce a magnetic field according to Ampere's...

Homework Statement Write the net ionic equation for H2SO4(aq) to the KMnO4(aq)Homework Equations The Attempt at a Solution I am confused on which one should i write. The first method is to list all the species, then use the data book to find which one is the strong OA and SRA. Multiply one or...

When you choose the co-domain can it just be anything that is greater than the range (i.e. the image)? In general, should the co-domain just be whatever space it maps to: R^2, R^3, etc. whereas the range is a subset of that space such as R^+ (all positive reals)?

So far I have learned these (correct me If I am wrong) A photon can be considered both an wave and particle. The wave equivalent of the photon is the superposition of Electric and Magnetic Field Waves. Similarly, De Broglie expanded this concept into matter. He proposed that Every matter has...