Confusing Definition and 407 Threads

Hi everybody, Last time I was here I was asking about finding roots but many things have progressed. Anyway I have another problem now. I have a linear system of equations which I'd like to solve: A.X==B And I tried two things: get the inverse of A and multiply it with B and also use...

A irreversible heat engine operating between heat reservoirs at 600 K and 300 K has half the efficiency of a Carnot engine. Calculate the entropy change of the working fluid in the engine which is the system, the surroundings, and the universe per cycle of the engine if 1000 J are extracted from...

Suppose f:[a,b]--> R and g:[a,b]-->R. Let T={x:f(x)=g(x)} Prove that T is closed. I know that a closed set is one which contains all of its accumulation points. I know that f and g must be uniformly continuous since they have compact domains, that is, closed and bounded domains. Now T is the...

We have a car stuck in the mud. To pull it out we have tied a rope on it and began pulling in one direction horizontally. Another method was proposed that one end of the rope was tied to the car and the other was tied to the nearby tree and then the same amount of force was applied perpendicular...

Homework Statement For which numbers a, b, c, and d will the function f(x) &= \frac{ax+b}{cx+d} satisfy f(f(x)) = x for all x (for which this equation makes sense. Homework Equations The Attempt at a Solution I'm not sure if the answer will consist of specific values, or just a general...

Hi First of all I'd like to say that I don't want to put this under "Homework help", because its not really homework. But it is something I can't wrap my mind around. There are 2 tasks: 1) There's 200 cm3 water in a glass. How high does the water level rise / how much does the cubage...

Homework Statement let A and B be finite sets Let P(A) denote the Power Set of A (set of all subsets of A)Homework Equations Prove or disprove: a) P(A inter B) = P(A) inter P(B) b) P(A U B) = P(B) U P(B) The Attempt at a Solution So I tried drawing Venn diagrams and came to the conclusion...

I am still totally confused about the principle quantum number even though i got passed the unit with a A+ on the exam. does the principal quantum number, n, have anything to do with the period? Does the "n" value, which leads to the "l" and "ml" actually indicate all the possible orbitals for a...

Homework Statement You are designing software for an anti-aircraft system. Your guns have a maximum horizontal range R, and can be fired at any angle (call it "A") above the horizontal. Enemy aircraft are spotted at time t=0, flying at altitude H, distance D, horizontal velocity V toward a...

Hi there, in the course of linear algebra, we talk about many on matrix and related properities. I wonder if any equations written in terms of matrices are linear? Could nonlinear equations also written in matrices? Thanks

So there is this guy named David Franklin Farkas of Amherst. His website is http://househealing.com . He "recently started a business psychically checking buildings for damage and repairing any 'holes' he finds in the energetic structure. It may sound like something from a sci-fi story, but...

Can someone please 'stupify' the definitions of an elastic and inelastic collision? Do objects bouncing off of each other undergo elastic collisions, while objects which stick together undergo completely inelastic collisions? This concept is very confusing to me :S thank you!

Homework Statement lim[x→-2¯(from the left)] x+2/sqrt(x^2-4)Homework Equations The Attempt at a Solution When I attempted this question I felt that the solution was that this is undefined and when i put it into my ti-89 it said that too. My friend argues that it's...

I understand that as the frequency of an electromagnetic wave increases, its refractive index decreases in a material. According to this, red light would have a higher refractive index than blue light (is my mistake here? why?). Since sinI/sinR = n (where I is the angle of incidence, R is the...

comb(x) (or III(x), or Shah(x), whatever you want to call it) is DEFINED as the infinite sum of delta functions. III(x)=\sum_{n=-\infty}^{\infty}\delta(x-nT) for some period T. We know that \delta(x-a) is the shifted delta function where a is some constant. We also know that \delta...

Homework Statement This should be easy but I can't find why. Why is the following true for 0<x<1, \lim_{n \rightarrow \infty}nx(1-x^2)^n = 0 Homework Equations The Attempt at a Solution I understand why (1-x^2)^n goes to zero, but the nx part is not bounded and seems to...

Hi I have been trying to learn dirac delta function. but its kind of confusing. I come across 2 contrasting definitions for it. The first one states that the function delta(x-xo) is infinite at x=x0 while the other states that delta(x-x0) tends to infinite as x tends to x0. Now both of them...

Homework Statement A watch has a second hand 2.0cm long. a) compute the speed of the tip of the second hand. b) What is the velocity of the tip of the second hand at 0.0s and 15s Homework Equations No Idea... The Attempt at a Solution I drew a clock...but I don't even know...

Homework Statement Two boxes are sitting side on a frictionless surface. The box on the left has a mass of 11kg and the box on the right has a mass of 17kg. If a 90-N force pushes on the 11-kg box from the left, what is the force exerted on the 17-kg by the 11-kg box? A) 55 N B) 43 N C)...

I have just starting learning relativity and I have still a problem with the definition and notation of tensors. So a (r,s)-tensor takes r vectors, s one-forms and gives a scalar. Then I understand that a (1,0)-tensor takes 1 vector (e.g. from V) and gives a scalar which is exactly the...

Dear physics forums I am an A-level physics teacher and I have built, admittedly, a VERY simple circuit. The problem is that I cannot explain its behaviour. It involves a metre long wire, twisted at the ends to form a loop, and incorporated into a circuit as shown below: (or attached)...

Mechanical Energy question (Skier going down a slope...confusing!) First of all, I apologize ahead of time if my question seems to be really simple, but I have been working on it for at least two hours and still no progress (which is why this post made so late lol). My class has been working on...

Homework Statement Solve the equation log x4 - log x3 = log 3x - log 2x I know the laws of logs and I cleared all the other log questions in seconds but I can't figure this one out Homework Equations I know that log x4 - log x3 is the same as log x4/x3 but what I was wondering is if...

In some textbook of fundamental electromagnetism, the relation between magnetic field \vec{B} and so called magnetizing field \vec{H} is \vec{B} = \mu_0\vec{H} But later on, they introduce a so called relative permeability \mu_r = \frac{\mu}{\mu_0} I might be wrong but my...

I am having some trouble understanding the concept of electromagnetic waves, I suppose because I expect them to be analogous to physical waves you can see or touch (such as on a string). Yes, I know one can actually see them at visible wavelengths, but that doesn't help because I don't...

Homework Statement A person is pushing an object of mass m along the ground with force F. The coefficient of kinetic friction between the object and the ground is (mu)k. The object is accelerating, but then the person stops pushing and the object slides to a halt. The person then starts...

Homework Statement A uniform rod (M 4.4 kg, L 0.827 m) starts at rest on a frictionless table. A point mass = 0.808 kg hits the rod at a right angle at speed 6.39 m/s. The block strikes the rod at a distance of 0.12 m below the center of mass, and stops. Assume the block does not stick to the...

Homework Statement A door with symmetry and of m 43.1 kg is 4.76 m high and 2.68 wide. The hinges are placed all the way on top and all the way on the bottom of the door. Find the absolute value of the horizontal force supplied by the bottom hinge.Homework Equations Sum of torques = 0 Torque =...

Homework Statement I'm doing calorimetry, and I have 34.73C and 63C. I need to subtract 63 from 34.73, and get the answer in Kelvin. Homework Equations The Attempt at a Solution I know you add 273 to Celsius values to get Kelvin, but I am not sure which of these methods is correct: 1...

Homework Statement A piece of cloth with irrelavent mass is wrapped around a 67.5 kg cylinder of radius 0.167 m. Joe holds the free end of the cloth. The cylinder is released from rest, and Joe pulls the tape upward at a speed that just prevents the center of mass of the cylinder from falling...

Homework Statement a) A 1.79 kg toy train accelerates constantly from 0.82 m/s to 3.43 m/s in 0.479 revolutions while traveling around a circular track of r 16.7 cm. Find: - α, magnitude of the angular acceleration.Homework Equations The Attempt at a Solution I first tried getting...

A confusing trigonometric question! Hi guys, I had a question. I was given the following equality. There was no problem statement that came with it (i.e. it did not say solve the equation or prove the identity, or anything of this nature) sec x + csc x / tan x + cot x = sin x + cos x The...

Homework Statement If the mass of an object increases, its momentum A. always increases B. always decreases C. sometimes increases, sometimes decreases D. sometimes decreases, never increases E. sometimes increases, never decreases Homework Equations MV=momentum The Attempt at...

1. http://paer.rutgers.edu/PT3/experiment.php?topicid=5&exptid=177 The three black stoppers that are whirling in a circle have a combined mass of 58.7g. The length of man's arm from elbow to wrist is about 30 cm. 2. Find the mass of the other object that is tied at the bottom. 3. I solved for...

Limit of ln(n)/ln(n+1) as n-->+infinity, very confusing can someone help me find the lim as n approaches infinity of ln(n)/ln(n+1) I used L'HOP so it became (1/n)/(1/n+1) -- as this approaches infinity, it's 0/0, and this confuses me. What am I doing wrong?

Hi. Recently day, I tried to solve quantum mechanics problem in liboff fourth version to prepare graduate school. But what make me be confused a lot is Dirac Delta Function. One of my confusing on Dirac Delta is what i wrote below. -One of the formula describing Dira Delta...

Do you find these creatures attractive? i think they have been made into a parody of what the chick/arty people think is cool. And the way they walk what the, who thought that up? And the clothes? a lot of them make the wearer look a real plonker. Yes i watched a fashion show on tv and...

Homework Statement A cannon fires a 0.626 kg shell with initial velocity vi = 9.6 m/s in the direction θ = 50◦ above the horizontal. The shell’s trajectory curves downward be- cause of gravity, so at the time t = 0.392 s the shell is below the straight line by some verti- cal distance...

Homework Statement A tank contains 1000 gal of water in which 200 lb of salt is dissolved. 50 gal of brine, each gallon containing (1 + cos t) lb of dissolved salt, runs into the tank per minute. The mixture, kept uniform by stirring, runs out the same rate. Find the amount of salt in the...

A helicopter is moving horizontally to the right at a constant velocity. The weight of the helicopter is W = 57600 N. The lift force L generated by the rotating blade makes an angle of 21.0° with respect to the vertical. (a) What is the magnitude of the lift force in N? (b) Determine the...

i thought i understand it but i guess i don't... you can expand a function in cosine f.s., sine f.s. and complete f.s. on some [0..L]. i thought that the coefficients a_n and b_n for complete expansion would come from sines and cosines respectively, but i guess that wouldn't make sense...

Hi everybody! This might seem like a terribly easy question, but I can't seem to figure it out for the life of me. I've been given a set of values for time and velocity: t (s) v (m/s) 0 0 3 7 7 16 12 33 18 48 23 53 27 67...

Here is a picture of the problem. The question is: A force F0 causes an acceleration of 17 m/s2 when it acts on an object of mass m sliding on a frictionless surface. Find the magnitude of the acceleration of the same object in the circumstances shown in each figure below. Figure (a)...

Dear all, P (A |B) + P (A c|B) = 1 [A c] denotes complement of set A and of course P (B)>0 Is the above statement true? How about the following two: P (A |B) + P (A |B c) = 1 P (C ∪ D|B) = P (C |B) + P (D|B) − P (C ∩ D|B)

Confusing projectile motion problem -- need guidance Here is the picture of the diagram. The Question: A woman throws a ball at a vertical wall d = 3.6 m away. The ball is h = 1.8 m above ground when it leaves the woman's hand with an initial velocity of 16 m/s at 45°. When the ball hits the...

hello.i have a weird problem. (-8) ^ (2/6) = ? my first instinct was to simplify the exponent, which yields (-8) ^ (1/3) = -2. this is the answer the calculator gives as well. but someone pointed out if you don't simplify that exponent, you have the sixth root of (-8^2), which would...

Homework Statement A rock is thrown horizontally from a cliff with a speed of 15 m/s. It falls half of the heigh of the cliff in the last three seconds of its fall. What is the total fall time? Homework Equations The Kinematic Equations The Attempt at a Solution Well here's what I...

arXiv:astro-ph/0310808v2 paper by Lineweaver dated 13 Nov 2003 entitled "Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the universe" has a sentence in the second paragraph on page 4 that I find confusing. The sentence is: "However, since...

to be able to understand my point of view please check this picture which I attched>> the question is in the picture please check it thanks

If I have a function f from RxR to R, and a function g from RxR to RxR. What are the partial derivatives of the composition f(g)? I end up multiplying the derivative of f with g, but g is a vector? The partial derivative should have its image in R.