Confusion Definition and 1000 Threads

I'm having some confusion with a couple trig identities. On wikipedia (http://en.wikipedia.org/wiki/List_of_trigonometric_identities#Product-to-sum_and_sum-to-product_identities), the following two identities are listed: sinθcosβ = (1/2)[sin(θ+β) + sin(θ-β)] and sinβcosθ =...

Hi guys, first off, thanks for answering my previous question... Now here's another one. I got confused by my school's homework a bit...so there's a car that travels over a humpback bridge with a radius of 45m, so basically it's a semicircle bridge, and so I'm supposed to calculate the...

Please can someone help me as I really don't understand the Michelson-Morley experiment - there seem to be (from what I have read) two different versions on it. Both versions assume the same apparatus where two light beams are sent out perpendicular to one another. One version says that if a...

If you consider a bullet firing from a gun then you have conservation of momentum and a Newton's third law pair (according to what i have read on the internet anyway). They both experience the same force if they are a third law pair but, generally, what is it that determines which object...

Hi I've just started learning work, energy etc and the first question in the book is in the form: An object of mass m is lifted by a tension through a displacement of h. Find the work done on the object. I know that the answer is simply mgh J, there is something that I don't quite get...

My school textbook says that discovery of the 1a supernova was what led to the understanding that the universe expansion is accelerating but doesn't hubble's equation already suggest that the universe would expand at an accelerating rate? V = Hd (V = velocity, H = hubble's constant, d =...

I will occasionally get problems wrong because the "right" answer should be y=nx, but I put x=ny, is the program being nitpicky or am I somehow misreading the problem?

I know that v(t)=dx/dt Then what is v(x) and how? Is it also dx/dt or something else?

After solving a DE I ended up with (y3)/(3x3) + ln(x) = c and initial conditions y(1) = 2. If I just plug in straight away I get (23) / (3(13)) + ln(1) = c which is c = 8/3 but if I multiply the equation by 3x3 first: (y^3) + (3x3)ln(x) = (3x3)c and the 3 goes into the c and solving for c I...

Homework Statement I have two questions. 1) The ends of a length of wire are labeled a and b. If the current i from a to b is negative, are electrons moving toward a or b? 2) We have a circuit element with terminals a and b. The voltage and current from a to b are both positive. If...

My physics core is a little bit weak, and this one question confuses me. Homework Statement A 3kg box sits on top of a 7 kg box. The object accelerates at 1 m/s^2. Find the force applied on the bottom block; if there are no forces besides this one. Homework Equations F= ma The...

Can anyone help me out with this? Here's the question 1. Homework Statement A 2.2 kg block sits on top of an even bigger 3.2 kg block. The coefficient of kinetic friction between the two blocks is 0.25. The coefficient of static friction between the 3.2kg block and the floor is 0.32 Find the...

Hi this is my first post... May be I am doing something wrong... I was thinking about a unit acceleration of 1ms-2 ,let an object be accelerating 1ms-2 and at rest the object's velocity was 0ms-1 and after 5 seconds its velocity was 5ms-1 ,so it will cover a distance of 15 meters after 5...

Hi! I am new here, thought to join as I am trying to learn Relativity, in this case Special Relativity. I have solved a bunch of problems already but ... The Lorentz Transform formulation I am dealing with is a 4x4 matrix. I understand the invariance of the spacetime interval and have...

Homework Statement Find vL(0+) Homework Equations V=IRThe Attempt at a Solution I have an exam tomorrow and so I'm in a bit of a hurry so please excuse the horrible drawing. The problem I'm having with this question is a conceptual one. I've found vL in this this circuit by first finding...

I am stuck on this one: According to me, the only correct answers are \vec{r} = \vec{t} - \vec{s} \\ \vec{r} + \vec{s} = \vec{t} But according to the key, these are also correct \vec{r} + \vec{t} = \vec{s} \\ \vec{s} + \vec{t} = \vec{r} I honestly do not see how, can somebody...

Dear all, I have been spending 12 hours on this and cannot seem to come up with a solution. We derive Helmholtz Free Energy (A) from the second law of thermodynamics. dS(Total) = dS(system) + dS(surrounds) we try to express dS(surrounds) with properties of the system. Assuming...

Homework Statement I'm confused about writing down the equation: \Lambda \eta \Lambda^{-1} = \eta in the Einstein convention. Homework Equations The answer is: \eta_{\mu\nu}\Lambda^{\mu}{}_{\rho}\Lambda^{\nu}{}_{\sigma} = \eta_{\rho\sigma} However it's strange because there seems...

I am recently going to undergo my second year in Computer Engineering and my dream job is to work in cyber security. I always thought that I could work in Cyber security with a major in Computer engineering but I have been told that it is Computer Science not engineering, but I heard this from...

Hi, I keep running my brain in circles while trying to get a solid grip on Noether's theorem. (In Peskin and Schroeder they present this as a one-liner.) But I'm having trouble seeing the equivalence between "equations of motion are invariant" and "action is invariant (up to boundary term)"...

Hello all, I an trying to size a motor to drive two mechanisms but am having some real trouble getting my head around the required torque. First let me explain what we have. Basically there are two mechanisms where I have plotted the speed and torque requirements on this graph as you...

Homework Statement Hi i got this question ? have to find Vr and VL so can i use this formula : VR = IR VL = I * XL? confuse ?? need help ?? am i on right track?

Homework Statement A house with floor space of 2000 ft^2 and average height of 9 ft is heated from an average temperature of 50 degrees F to 70 degrees F. Determine the amount of energy transferred in the house assuming: a) The house is air tight. b) Some air escapes through the cracks as...

During electrostatic induction,a posivitiely charged body is brought near to a uncharged body.During this uncharged body gets bound negative change toward the end of the body near to charged body. My question is in reality what happens to the electron and proton of uncharged body.Do the all...

please help! The formula for kinetic friction acting on a sliding body is μkN When the body is sliding with constant velocity down an inclined plane fk=μkN When the body is sliding up the inclined plane(say due to a force acting parallel to the inclined plane) with constant velocity...

consider a pendulum. The mass 'm' is hung and now we are interested in finding the velocity so that it completes one circle. Clearly we can do it easily by conserving energy. Now my problem is with the top most point. Clearly the tension is minimum at this point so that string becomes slack...

I'm familiar with the differential form of Gauss's Law, which reads that ##\nabla\cdot\vec{E}=\frac{\rho}{\epsilon_0}##, where E is the electric field, ρ is the charge density, and ##\epsilon_0## is the permittivity of free space. We can take the volume integral of both sides, and then use the...

In the derivation of drift velocity i have seen two variations and want to know which one's correct. s=ut +\frac{1}{2}at^{2} Assume that the drift velocity of any electron in any conductor is : v_{d}=l/t Due to the electric field the acceleration of electrons in any conductor...

Regarding the post below in http://www.mathhelpboards.com/f10/epsilon-delta-proof-confusion-4745/: There are just two things left I need to wrap my mind around, after that I think I will have comprehended the epsilon-delta concept. In example 3 in the document epsilon-delta1.pdf where the...

Hi folks First off I have only just figured out that v is used as bloody frequency in loads of astrophysics equations. Not fun. I've got monochromatic flux as: Fv = dE / dt·dA·dv now I'm happy with this. But now the lecture notes I'm looking at describes monochromatic luminosity as...

In a epsilon-delta proof, one wishes to show that $$0 < |x-a| < \delta$$ implies $$|f(x) - \text{L}| < \epsilon$$. But every example that I have seen, one always begins with the "then"-part, namely the conseqeunt $$|f(x) - \text{L}| < \epsilon$$, and work backwards to arrive at something...

Hello, I am having some difficulties understanding why a subset under the usual metric topology of the reals is connected. How can a set X = (0,1] u (1,2) be connected? The definition I am using is: A is disconnected if there exists two open sets G and V and the following three properties...

This is a very basic problem which you all must have seen somewhere. But recently an itching doubt has come up to me regarding this problem. Problem: A chain lies on a table with some part of it hanging over the edge. Now if the coefficient of friction is μ, then find out the maximum part...

Hi, So f(x,y) = xe-x(y2 - 4y) Find all stationary points and classify them i got for fx(x,y) s.p (1,4),(1,0) for fy (x,y) s.p (0,2) I thought that you don't need double differentials at this stage and if it is a s.p it must satisfy for fx(x0,y0) = 0 for fy (x0,y0) = 0 which...

I'm just having trouble understanding some of the notations given, when attempting questions such as the following: {f\inF(ℝ,ℝ): f(3)=5}. Is it just saying that, the function 'f' spans all real values?

Hi there, So regular i thought that the procedure was F(s) = ∫s0 f(x) dx However i am doing a problem with a kinked pdf and it is telling me to do something like F(s) = ∫s0 f(s) ds for 0=<s>=1/2 then... F(s) = F(1/2) + ∫s1/2 f(s) ds I am confused at the process of using f(x) or...

(I am a newbie in physics. I did not use the template when posting as this isn't really a homework question but about something that makes me confused in elementary physics). Suppose I have two objects (with masses m<M respectively) connected vertically by a wire such that the one with mass m...

I'm having trouble understanding the ratings for an SPST Relay. I need one with the following specs: Coil Rating: 12Vdc, Contact Rating: 20Amps @ 15Vdc If I use a relay with a 24Vdc Coil rating, does that mean that it would require 24Vdc to operate, or is that the maximum amount of...

I'm confused about the the definition of a function not being continuous. Is it correct to say f(x) is not continuous at x in the metric space (X,d) if \existsε>0 such that \forall\delta there exists a y in X such that d(x,y)<\delta implies d(f(x),f(y))>ε Is y dependant on \delta? It...

The expositions for a normal probability plot (aka normal quantile plot) (in which observed probabilities are plotted against theoretical probabilities, or sometimes the other way around, to get a rough check as to whether a set of data is normally distributed by checking linearity) are not too...

I know there must be something wrong with the following derivation based on Maxwell's equations but could not figure out what is wrong. The derivation deals with continuity of current and free charge in a conductor in general. Continuity of current says that, \nabla\cdot...

I understand that there are 4 fundamental "forces" of nature that we've identified; gravity, electromagnetism, and the two nuclear forces. However, I have been under the impression that gravity isn't a "force" in the same way that the others are. From what I figured, a force is something that...

Hi everyone. I'm working on deriving Friedmanns Equations from the Einstein Field Equations. I've got the '00' components worked out but I'm having some trouble with the spatial indices 'ii' of the stress energy tensor ## T_{ii} ##. I'm the FLRW metric with c=1 and signature (-,+,+,+) so that...

Homework Statement Engineers perform a crash test with a minivan and a compact car. The mass of the minivan is 800kg and the mass of the compact car is 560kg. The minivan was moving north, and the compact was was moving east. After the collision, the two cars crumpled together and moved at...

I've seen an experiment with a light clock that explains time dilation. A photon is fired and gets reflected off of 2 parallel mirrors. It keeps bouncing back and forth like that, with each bounce qualifying as one tick of the clock. And it looks like that from a stationary reference frame. Now...

Homework Statement f(x)=\frac{4x}{(4+x^{2})^{2}}Homework Equations \frac{1}{1-x} = \sum x^{n} The Attempt at a Solution How am I supposed to use that equation to solve the main problem. I have the solution but I don't understand how to do any of it. My professor is horrible, been on...

Homework Statement For each material calculate the cross sectional area in m². Each sample is of rectangular cross section 20mm by 1mm. Produce Stress and Strain tables for the data. TEST DATA FOR X (N) EXTENSION (mm) 1000 0.48 2000 0.60 3000 0.70 4000 0.80 Homework...

I've just started reading Arfken's book on mathematical methods for physics, and one of the very first sections is really confusing me. He is discussing the rotation of coordinates, and defining a vector as an object whose components transform in the same way as the coordinates do under a...

Hi All, I'm trying to implement the Gaussian Mixture Model for background subtraction as described by Chris Stauffer and W.E.L Grimson in their paper "Adaptive background mixture models for real-time tracking." I'm having a little trouble with the logic in the step that updates the mean...

Hello all, I am so confused on why a net torque on a dipole in a uniform electric field would not be equal to zero. Wouldn't one end rotate clockwise, the other counterclockwise and cancel out to zero? Thanks.