Sign Definition and 579 Threads

Homework Statement You are holding a sign as shown below. The sign (including the horizontal bar it hangs from) has a mass of 2.20 kg and is 40.5 cm wide. The sign is hanging from a 1.03 m tall, 4.46 kg vertical post. The sign is symmetric with a uniform mass distribution as implied by the...

Homework Statement why there is - sign in front of integral of (z2-z1)dA , is it a mistake ? Homework EquationsThe Attempt at a Solution

I have a toy quantum circuit simulator that I work on. I want to visually represent operations in multiple ways: as a Hamiltonian, as a unitary matrix, and as a Bloch sphere rotation. I want to double-check that I haven't flipped anything. I'll focus a concrete example: is this animation...

Homework Statement A 14.0 kg sign hangs from 2 lengths of rope, each of which is 70.0 cm and at a 20.0 degree angle from the ceiling. 1) What is the tension of the rope? 2) How could you reduce the tension on the ropes for the same sign without adding another rope? Homework EquationsThe...

Hey all, this is my first post here (so please let me know if I posted this in the wrong place). In school, I won't be able to take the AP Calculus BC exam even though I am self-studying calculus right now (long story). As a result, I am planning to sign up for the exam on my own. The College...

Homework Statement Water flows from the faucet on the first floor of the building shown in the figure with a maximum velocity of 20 ft/s. For steady inviscid flow, determine the maximum water velocity from the basement faucet and from the faucet on the second floor. Assume each floor is 12 ft...

Homework Statement A combination circuit powered by a 6.0 V battery is shown. What is the total current through this circuit? I don't know how to determine where the signs go, for example if the right side of a resistor is positive or the left side is positive Homework Equations What is the...

I was doing the following problem: And I was asked to find Iy. I found Iy to be 2.64 using KCL. However, the right answer was negative 2.64. Is it negative only because there is a dependant voltage source with "+ -" ? And why must it be negative? Does "-" in the final answer play a...

Homework Statement a) Find the net electric field at a point b) Find the net force experienced by a charge of -1.2 x 10-5 C placed at that point c) What would happen if the charge changed signs? Homework Equations FE = qε The Attempt at a Solution a) Solved: 6.7 x 104 N/C [E 63° N] b) FE =...

I(α) = 0∞∫e-(x2+α/x2) dx Differentiating under the integral sign leads to: I(α) = 0∞∫-e-(x2+α/x2)/x2 dx Here I am supposed to let u = sqrt(a)/x, but the -x2 doesn't cancel out, Wolfram-Alpha tells me the answer is: e(-2 sqrt(α) sqrt(π))/(2 sqrt(α)). I understand where the sqrt(π))/(2)sqrt(α)...

Okay so after reading various books on sign conventions for work I am told by my teachers that in chemistry,work done on the system is positive while work done by the system is negative while in physics it's the exact opposite I only use the former convention And modify the first law of...

This isn't actually a homework problem, but it is an example in a my textbook that I have a question about... imgur link: http://i.imgur.com/2OglMH4.png Ok, I wanted to clarify some things. I understand that current flowing from a positive terminal to a negative terminal represents a...

Hi! I am looking for some guidance as to what statistical tests I would need to do to know the significance of a study. The situation is this: Disease in Question is Sinusitis Gold Standard for Diagnosis is CT, but is seldom done as not all cases require confirmation. Cost-effectiveness...

I'm an applied mathematician with lots of experience in classical physics but none in quantum physics. What's the simplest piece of code (eg C++ on Cygwin) that illustrates the https://en.wikipedia.org/wiki/Numerical_sign_problem in quantum physics?

Why would an inequality sign flip in an answer. For example: 16 < -s -6 The answer is given s < -22 I had -s > 22 I am thinking it is because when you x by -1 to keep from having a negative variable the inequality sign flips...is this why?

I am making a sign out at my farm. I am making everything myself and have come up with an idea on getting the letters to stick to the front of the sign with magnets. I just have plastic letters with magnets glued to the back and they just stick on the front of the sign that has a galvanized...

My question arises from trying to get the correct sign convention for a pulley that has two boxes attached by a massless rope. one box is to the left of the pulley and the other box is hanging down below the pulley. If I take the counter clockwise direction to be negative, and set up my...

I'm not sure whether to put this here or in Linear Algebra, if any Mod feels it should go in Linear Algebra I won't mind. I've just been introduced to Fourier Series decompositions in my Linear Algebra text, and I understand all the core concepts so far from the Linear Algebra side of it (a...

Equations I used: Fty = Ft(sinθ) Ftx = Ft(cosθ) My attempt: I drew a free body diagram that looked like this (the red are just components of the tension, I know they wouldn't usually be included on a free body). Finding Magnitude of Tension: Fg = 516 (I gathered from the problem) Fg = Fty...

Hey guys, So just completed a question on a sign post subject to wind loading of 2 kPa where you had to determine bending moments across x and z planes (picture below), to determine normal, shear, max stresses and then determine the factor of safety depending on the beam type you chose. That's...

In the derivation for equation 24-2 in the picture below., the line integral was chosen along a path anti-parallel to the field lines. As a result, cos(180) = -1, which made the integral for the voltage positive. However, in examples 24-2 and 24-3, the line integral is also taken as...

If the work done by an electric field is N, then the work done by me will be negative N? Perhaps this applies if I move a charge against the field lines, but what if I move in the same direction?

I was wondering if anyone knew the standard notation for the following. Suppose I have functions ##f_1,f_2 \ldots,f_n##, is there a compact way of writing ##f_1 \circ f_2 \circ \ldots \circ f_n## ? I am debating whether ##\bigcirc^n_{i=1} f_i## is proper or good notation. Have anyone encountered...

In March, Playboy magazine will roll out a new design which lacks the fully-nude photos that have been a signature feature since its beginning in 1953. Hef himself agreed to the change. Nudes Are Old News at Playboy (New York Times)

I know this is probably the least of my worries at the moment but my quantum textbook solves ##\frac{\mathrm{d}\phi (t) }{\mathrm{d} t}=\frac{iC}{h}\phi (t) ## as ##\phi (t) = e^{-i(\frac{C}{h})t}##. Is this not off by a sign? Its really bugging me.

This is a general question that i am confused about. If I throw a ball up, then is the distance that it reaches at the very top the y or y-initial? Also, is this y or y-initial positive or negative?

[I asked this question over a year ago, but I thought I'd try again.] Let ##I\subseteq \mathbb R## be an interval and ##f:I\to\mathbb R## be a ##C^\infty## function. I have the following characterizations: 1) ##f'\geq 0## everywhere iff ##f## is increasing. 2) ##f''\geq 0## everywhere iff...

Hi , this may been asked quite a bit times but I can't really find a solid answer for this. Do we have to include negative signs during calculations for vectors or scalars? I have been told by someone that for vector quantity calculations such as Force we do not include the negative sign or...

This question is motivated by one on stack exchange, and on this paper (which comes across a bit student-y but it claims to have been reviewed, and in any case I have reproduced its results in ctensor and gnuplot). So: the KS (abbreviation!) conveys an overview of curvature at a given point in...

Homework Statement Consider the fermionic part of the QCD Lagrangian: $$\mathcal{L} = \bar\psi (\mathrm{i} {\not{\!\partial}} - m) \psi \; ,$$ where I used a matrix notation to supress all the colour indices (i.e., ##\psi## is understood to be a three-component vector in colour space whilst...

I'm trying to understand how electric generators work on a very basic level. I understand the heart of this is the application of the Lorentz force on a conductor moving at a velocity ##v## in the presence of a magnetic field ##B##. I also understand how it can be shown that the emf is equal to...

Homework Statement For an s-polarized wave (E and B fields are orthogonal to the plane of incidence) passing from medium to medium 2, I'm not understanding a minus sign. The matching conditions are ##\hat n \times (\vec E_2 - \vec E_1)=\vec 0## and ##\hat n \times (\vec H_2 - \vec H_1 )=\vec...

Thought I knew this, but am confused by the following example: Show $ |z^3 - 5iz + 4| \ge 8 $ The example goes on: $ |z^3 - 5iz + 4| \ge ||z^3 - 5iz| - |4|| $, using the reverse triangle inequality It's probably right, but I don't get why the +4 can just be made into a -4 ?

Homework Statement A 30 kg neon sign is suspended by two cables, as shown. Three neighbourhood cats (5.0 kg each) find the sign a comfortable place. Calculate the tension in each cable when the cats are in the positions shown. Ft1 = tension in left cable Ft2 = tension in right cable...

what does this --> ∫ mean and what how do you use it? Thanks.

Why Maxwell's stress tensor has minus sign to the corresponding components of electromagnetic momentum energy tensor ? From WP --- , where , is the Poynting vector, is the Maxwell stress tensor, and c is the speed of light. ----

I want to know the sign of the cosmological term. It seems that in the left hand side of the Einsetein equation the cosmological term is -\Lambda g_{ik} for (+---) convetion or +\Lambda g_{ik} for (-+++) convetion. Right? Best

The authors of a physics textbook want to determine the number of grains, N in a beach of 500 m long, 100 m wide, and 3 m deep. They assumed that each grain is 1-mm-diameter sphere. They also assumed that the grains are so tightly packed that the volume of the space between the grains is...

Homework Statement given a continuous-time signal g(t) . Its Fourier transform is G(f) ( see definition in picture / "i" is the imaginary number) . It is required to find the Fourier transform of the shifted-time-reversed signal g(a-t) where a is a real constant . That is , find the Fourier...

I have a block with a certain mass attached to a spring. I pull it and then release. Spring pulls block back. When spring is back to its relaxed position, is the velocity of the block positive or negative? Exercise does provide k, mass and x, but that's not where the error is comming from...

Why is it not just dE = q + w because I assume if you use general sign convention and take work to be negative when it is done by the system and positive when it is done on the system, you should get the right answer. Silly question but I'd appreciate some clarity on this formula please?

Homework Statement Actually I have two doubs, the first one is Why in the solution of this problem, in the sumatory of moments in C, Force 2=10?? If in the sumatory of moments in F, Force 2 is 416.7 N. Actually I calculate with 416.7 N, and T in C = 100 N. The other doubt is with the sign...

Hi, I am trying to solve a model where Non-interacting Green functions take part it. It has happened something that is spinning my head and I hope someone could help. The non interacting Green function for a chanel of electrons is...

Hi! I have learned that the Hall-coefficient changes sign according to different metals. Copper for instance has a positive sign, while Zinc has a negative sign. Why? To me an ordinary non-doped metal should always have electrons as beariers of charge. Further more, I have learned that...

I was reading through hobson and my notes where the covariant acts on contravariant and covariant tensors as \nabla_\alpha V^\mu = \partial_\alpha V^\mu + \Gamma^\mu_{\alpha \gamma} V^\gamma \nabla_\alpha V_\mu = \partial_\alpha V_\mu - \Gamma^\gamma_{\alpha \mu} V_\gamma Why is there a minus...

Homework Statement I'm trying to figure out why potential energy decreases in this situation http://imgur.com/9PfjRVE Homework Equations ΔU = FΔy The Attempt at a Solution If I define up to be positive, and ΔU = FΔy. In this picture, force is pointing down (so it is negative) and the height...

Comparing two sources one has ##\frac{d^{2}x^{i}}{dt^{2}}=-\frac{1}{2}\epsilon\bigtriangledown_{i}h_{00} ## and the other has ##\frac{d^{2}d^{i}}{dt^{2}}=\frac{1}{2}\epsilon\bigtriangledown^{i}h^{00}##, And the one using the lower index has the Newton-Poisson equation as ##...

In physics book, if work is done by the system, it is positive in my chemistry book, if work is done by the system, it is taken as negetive. when I asked my chemistry teacher, he said the sign convention is different in physics and chemistry. but why are they different?

http://www.mth.uct.ac.za/omei/gr/chap7/node3.html Shouldn't eq 45 have a minus sign, looking at eq 29. Although I'm confused because the positive sign makes sense when comparing with the Newton-Poisson equation. I can't see a sign error in eq 29. (I believe the metric signature here is...

Homework Statement You are holding a sign as shown below. The sign (including the horizontal bar it hangs from) has a mass of 1.80 kg and is 36.5 cm wide. The sign is hanging from a 1.30 m tall, 4.16 kg vertical post. The sign is symmetric with a uniform mass distribution as implied by the...