Confused Definition and 1000 Threads

Homework Statement Let f be a vector function, f = (xz, 0, 0), and C a contour formed by the boundary of the surface S S : x^2 + y^2 + z^2 = R^2 , x ≥ 0, y ≥ 0, z ≥ 0 , and oriented counterclockwise (as seen from the origin). Evaluate the integral (Closed integral sign) f · dr , directly as...

confused, project is due in 2 hours, can someone please help , thanks.

Perturbation-the ability of an unperturb system to remain the same when a perturb system is added to it. Can't really understand this?

I had always thought that the concept of rotation required it being around an axis rather than a point, but now that I have been exposed to using vectors to represent rotation, I am a little confused. Angular momentum is defined as the position vector cross the linear momentum vector. Suppose a...

Say for instance a + charged particle is moving right along the x-axis. Then it will encounter a magnetic field with the direction pointing up. Using the Right hand rule, the force acting on that particle will be going out of the page to me so to speak. But what if it was an electron with a...

Homework Statement what is the identity of a3 + b3 + c3 i am getting a bit confused please help! Homework Equations The Attempt at a Solution

I'm confused about the sum of the geometric series: \sum ar^{n-1} = \frac{a}{1-r} when |r|<1 but if you have a series like: \sum (1/4)^{n-1} the sum is: \frac{1/4}{1-(1/4)} should't it be \frac{1}{1-(1/4)} because there is no a value?

So 1 pascal is 1 Newton per squared meter Are 2 pascals 2 Newtons per squared meter, or 2 Newtons per 2 squared meter applied on the object?

Hi, I'm a double-msc in engineering, now a 3rd year phd student in maths. My main specialty is scientific computing in C++. I got an offer for a 4-6 months internship in a very interesting company, and I don't know whether to accept. Between the decrease in my income (I have to take a leave...

When proving by smallest counterexample, you assume an integer k>1 where it is the smallest integer for which statement Sn is false. Then you proceed to prove that Sk-1 implies Sk. Where you deduce a contradiction by which k is true. Can't you prove this directly by assuming Sk-1 is true and...

Can someone tell me (when RREFing a matrix) when do we put the vectors of a subspace in columns of a matrix and when in rows? Example from my notes: Here, my prof put the vectors in columns: and here, he put the vectors in rows: Thanks!

Hi! I am new to these, and off the bat am confused by the units. Manufacturers quote resolution either in units of length, e.g. 0.04 nm, or HZ. For example, 0.04 pm / 5MHz 0.16 pm / 20 MHz 0.8 pm / 100 MHz. I am thrown by this since I thought frequency was the inverse of...

High School senior confused in life... :( :confused: I was wondering if anyone had any insight as to which career path I should take? I am interested astronautical engineering, because of my love of space and designing spacecraft seems incredibly interesting and fun... It would be a...

Homework Statement what is the kinetic energy of a 3000lb car traveling at a 60mph (pounds are not units of mass) Homework Equations KE=1/2* mass * velocity ^2 The Attempt at a Solution pounds are the units of force but to calculate the mass I am missing some data unless I'm...

Hi, I'm currently studying some introductory discrete control theory and I've run into a problem with the Z-transform, although I could pose the same question regarding the Laplace transform. I know I'm completely off with this question but I've just stared myself blind to it. Here goes: I...

I am confused when it comes to this AC circuit problem. It is part e. The back of the book shows that V_R3 = 100 V. But as you see from my calculations, I get V_R1 = 20 V and V_R2 = 100 V. So shouldn't V_R3 = 0 V because the original voltage source for this AC circuit is 120 V, yet the book...

This is not homework even thought this is an example in the book of Griffiths "Introduction of Electrodynamics" 3rd edition. This is a mix retarded field and Poynting theorem question: \vec E \cdot \vec J \;=\;-\frac 1 2 \frac {\partial}{\partial t} ( \epislon_0 E^2 +\frac 1 {\mu_0} B^2)...

Ok so for a sequence x(n) to be bounded it means |x(n)|<=M but according to by book, if x(n) belongs to some closed interval, say [a,b], x(n) is bounded. That is confusing because say x(n) belonging to [a,b] means a<=x(n)<=b. How can there exist a M such that -M<=x(n)<=M? this means...

I have a basic question on my prelab. The professor wants us to make a graph of of a experiment where the volume of methane gas was measured at various pressures. The temperature is held constant. She gives us data for this experiment and wants us to make a graph for it as practice. I can dot...

So the definition states.( For any epsilon>0, there exists a delta>0 such that 0<|x-a|<delta => |f(x)-L|<epsilon. ) is equivalent to lim f(x)=L for x->a. Well say f<=C some constant. (reads less than or equal to) then L<=C But that means that the epslion neighborhood can't...

Homework Statement A spherical body is rolling on a rough surface. then "the frictional force may or may not be zero" Is this statement is correct or not? we discussed about this in classroom. Some were saying it must not be zero and others were saying it may be zero. Which is correct?

Hi, ok so everytime I think that I have understood the concept of Energy transmission, losses and voltage drop, I get even more confused about things. I have searched several threads on this forum and the physics forum but failed to find anything that directly answers my query. So I...

Number theory: confused about the phrase "an integer of the form" Homework Statement Prove that any prime of the form 3k+1 is of the form 6k+1 Homework Equations The Attempt at a Solution I'm not sure where to start at all. I tried rewriting 3k+1 as 6k+2=6k+(6-4)=6(k+1)-4. But...

Greetings all, I'm looking at some examples in the Topology: Pure and Applied text. Looking at example 2.1 Consider A=[0,1) as a subset of R with the standard topology. Then Aint=(0,1) and Aclos=[0,1]. Can someone explain to me why the union of all open sets in A is that...

Hello Guys! I was designing copper bus-bars which can withstand 1 kA current. Actually I am going to discharge a several DC capacitors into those bars. So, I was confused in the dimensioning the cross section. Is 25mm * 3mm cross section enough? I have made my calculation using 1.6 A/mm2...

Homework Statement A 25pF parallel plate capacitor with an air gap b/w the plates is connected to a 100v battery. A Teflon slab is then inserted b/w the plates and completely fills the gap. What is the change in charge on the positive plate when the Teflon is inserted? Homework Equations...

Homework Statement The equation 2y'' - y' + y^2(1-y) = 0 is a special case of an equation used as a model for nerve conduction, and describes the shape of a wave of electrical activity transmitted along a nerve fibre. Find a value of the constant a so that y = (1 + e^(ax))^(-1) is a...

I do not understand how On, the class of ordinals, can be included in the universe of an inner model of ZFC such as < V\kappa, epsilon>, where \kappa is the first inaccessible ordinal. My confused attempts to do so have led me to believe that I am getting off on the wrong foot in my analysis...

Visual field defects. Totally confused. Please help! Hello everyone, [PLAIN]http://img827.imageshack.us/img827/2756/picsds.gif I'm totally confused with this. If there is a lesion in A, why can't you see the left visual field. According to the arrows, if there is a lesion at A, you would...

I learned that the light is 100% linearly polarized when one looks at the angle shown in pic1. But when taking a photo of a blue sky and also in polarization navigation, it says that we look at the direction of 90 angle from the sun ray cos it's the region of maximum polarization. (pic 2)...

Tom and Victoria are two children who live in Canada. Consider the following dened events about two Canadian cities far from each other: Toronto and Vancouver.  Let T represent the event that Tom lives in Toronto.  Let V represent the event that Victoria lives in Vancouver. 1. If Tom and...

Can anyone guide me ragarding the difference between excitation, de-excitation and ionization. I just confused with the terms de-excitation and ionization, wether they are same..please guide me..

I want to verify my understanding about skin effect and plane wave of conductor wire. In the diagram, assume long straight on z axis. Wire with radius = a and conductance = \sigma . Accouding to the equation shown, the plane wave is going towards the center of the wire only...

Hi I'm trying to get a better understanding of dispersion in light. Specifically, the relationship between refractive index and wavelength, and why the refractive index increases for decreasing wavelengths. However, I've been confused by all the various information I've come across...

I'm confused about how to think about wavelength for something physical, like a simple pendulum or harmonic oscillator. I understand graphically what wavelength is but can't seem to come up with a physical description. I was thinking about ocean waves and that wavelength could be the direct...

I never understand the difference between 'Equally Likely Events', 'Mutually Exclusive Events' and 'Exhaustive events'. I also get confused in calling an event to be of more than one type. I would be grateful if someone explains it clearly giving examples.

Hello, I quote http://en.wikipedia.org/wiki/Precession from the first paragraph from the first section ("Torque-free precession"): But isn't the matrix product L = Iωs relative to the moving frame (that's how we did it in our course anyway), meaning L and omega are indeed the vectors as...

Homework Statement At 3 pm a rocketship passes extremely close to the Earth with a speed of 0.800 c. Observers on the ship and on Earth agree that it is 3 pm. At 3:40 pm, as indicated on the rocketship clock, the ship passes a small space station that is fixed relative to the Earth and...

I am confused about the usual derivation of the ideal magnetohydrodynamic equations, as given for example here: http://theoretical-physics.net/dev/src/fluid-dynamics/mhd.html The problem is that there are a few different "currents" to consider. For example, in the momentum equation, the...

Homework Statement say a[5] = { 5.6, -3.2, 11, -7.7, -1 ); and b = 5 void fum ( double a[], int b ){ for ( int i = b -1; i >= 0; i-- ){ if ( a[i] < 0 ) cout << -a[i]; else cout << a[i]; cout << ", "; } } Why is the output 1, 7.7, 11, 3.2, 5.6 and not 7.7...

I've been thinking about blackbodies, and have become confused with regards to their temperature. Is the temperature constant throughout in a blackbody, or is there a temperature gradient dependant on which side is closest to the source of heat? Would it matter?

Homework Statement The rope of a swing is 2.90 m long. Calculate the angle from the vertical at which a 81.0 kg man must begin to swing in order to have the same KE at the bottom as a 1450 kg car moving at 1.05 m/s (2.35 mph). Homework Equations KE=1/2mv^2 PE=mgh SOH CAH TOA (trig...

Vectors question- CONFUSED! Blabla

Homework Statement 2. The attempt at a solution Ok. so I'm a little bit confused as to how to approach this problem. I would know how to do this problem if it was laying right to left, but because it's vertical, that makes it a lot more confusing for me. I know A = (1/4)(pi)(d^2) =...

I was reading about worm holes and stuff like that, and I don’t get it. What dose going back in time really mean? If it just changes the time, how dose that all of the sudden give you the power to... kill your grandfather and create the Grandfather paradox, or walk around in the past... It...

Hi I've been working through some examples from the course material we use in physics class, but one thing keeps confusing me: What is the difference between centripetal and radial acceleration? For instance, when we have a particle traveling in a circular path, the acceleration towards...

Hi I got a question regarding conservation of mechanical energy. The mechanical energy of a system is conserved, as long as there are no transfer of energy (like heat, work, mechanical waves etc.), right? So, why is the mechanical energy in the system of the pivoting rod and the earth, as...

Hey everyone. I'm a senior in high school and need some serious guidance for my future major and job. I can say that I'm a very good student, academically, yet I lack the passion for anything right now. I want my knowledge to be powerful, on a level where it impacts the world. There are very...

Homework Statement QUESTION 1: Calculate the rotational moment of inertia of a meter stick, with mass 0.56 kg, about an axis perpendicular to the stick and located at the 20 cm mark. Treat the stick as a "thin rod." Homework Equations I=m(l)^2 BUT SINCE IT ASKED TO consider the...

Hello, My course is a bit vague on this topic. 1 First of all it states: if the differential equation A(x)y''(x) + B(x)y'(x) + C(x)y(x) = 0 with A, B, C analytical has A(a) = 0 but B(a) and C(a) NOT both zero, then a is a singular point and we can't solve it with a power series. Now: what...