Confusing Definition and 407 Threads

Dear PF Forum, I'm interested in the future. How mankind will benefit from fusion power. But there are some terms that I don't understand. Electron Volt. https://en.wikipedia.org/wiki/Electronvolt Volt https://en.wikipedia.org/wiki/Volt Perhaps this yes/no question will confirm my confusion...

Homework Statement Let's say I am pushing a couch with 30 N, the velocity is constant, therefore, the friction is also 30 N but in the opposite direction. But if a push it with 50 N then the friction force is going to change to 50 N as long as it is not accelerating. So how am I supposed to used...

Homework Statement The picture of the question is given Homework Equations simple motion equations The Attempt at a Solution [/B] I am so confused so I can't solve the question

I am trying to undersand Ashcroft's derivation of energy density on page 38. I am following most of the arguments save EQ 2.30. Where did the vector go? I did follow my professors argument for converting to polar/spherical when the argument of a function is a modulus of a vector — exploiting...

I have this question on my practice test that I can't figure out. "Just as one jumps out of a plane what is their gravitational force given that the mass is 70kg." The thing is, for me to use the gravitational force formula I need to masses. The test only has the one. Am I missing something? Am...

Homework Statement Look I have an exercise about trusses in vector mechanics. It's the following: https://scontent-lax3-1.xx.fbcdn.net/hphotos-xfp1/v/t1.0-9/12003339_1645511085733429_8210043018491702007_n.jpg?oh=4955534403fb6f3f5f9a40c9c0b8ecbc&oe=569761ED I have to determine the forces in...

I see I am not the only one finds Hilbert confusing - because all it's properties seem so familiar. I have gathered together what I could find, please comment? A Hilbert space is a vector space that: Has an inner product: • Inner product of a pair of elements in the space must be equal to...

I know that when we have to identify the nodes for solving a circuit with nodal analysis we always have to designate a reference node (which will be the ground node) as a reference for measuring the others' voltages. However I was practicing this and I found this example on...

Good evening people. Recently I started taking the "electric network analysis" course in my school. We already saw the mesh analysis method for solving circuits. Now we are seeing the node analysis method. I understand that the first step for this method is finding the number of nodes (and one...

Homework Statement Well I am looking for the particular integral of: d2y/dt2 + 4y = 5sin2t The attempt at a solution As f(t) = 5sin2t, the particular integral yPI should look like: yPI = Acos2t + Bsin2t dyPI/dt = -2Asin2t + 2Bcos2t d2yPI/dt2 = -4Acos2t - 4Bsin2t Subbing into the differential...

This may be a little of a stupid question. But I was looking at a diagram describing Bragg's Law of Diffraction. and I was like...how can an interference happen if wave beam C and wave beam C' are hitting different points on the detector screen?! they are not hitting the same point on the...

So,while learning mechanics,I found that most questions use g=-9.8 ,but when calculating the velocity the instant a rocket touches the ground,the solution instead used g=9.8,which is very confusing.Other questions of similar workings used g=-9.8,anybody care to help?

Hi! Not sure if this is properly categorized,please correct me if it isn't. What if deja vu is just our brain misinterpreting 'reality' and exposing us to spacetime. Like skipping ahead in time(according to the definition of time in spacetime) but then it calibrates us back into the present...

Homework Statement design a common-emitter amplifier with an output impedance of 4.7kOhms and again of-10 using a transistor with a beta=200 powered by a 12V DC supply. Homework Equations v=ir The Attempt at a Solution ------------------------------------------------------ rest of the...

I'm taking Physics 121 with an instructor that I personally find confusing. Nothing in the lectures nor explanations during office hours get through to me at all. Our assigned text is "Physics, Volume 1 - Resnick, Halliday, Krane." I want to get a solid foundation of the material (beginning...

I'm a bit confused on how to apply contrapositives... This isn't for homework but I'm attempting to show that if n^2 + 2 is prime that 3|n. I'm wondering if this is an appropriate time for me to show the contrapositive of the statement to be true, therefore the original statement to be true...

Suppose a change of basis from basis ##B## to basis ##C## is represented by the matrix ##S##. That is, ##S## is the transformation matrix from ##B## to ##C##. Now if ##t## is a given linear transformation, ##t:~V\rightarrow V##, with eigenvectors ##\epsilon_i##, say, and ##T## is the...

I am reading a book about quantum mechanics and the author is trying to show how the uncertainty principle can be obtained from the Schwarz inequality. Without going into the whole thing there is one point I get stuck following what he is doing.We have an operator called DA. We start with DA =...

Hi all, I was looking through this proof and have no idea where the "u" comes from., any help apreciated. http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++&bg=eedbbd&fg=000000&s=0 http://s0.wp.com/latex.php?latex=%5Cdisplaystyle++&bg=eedbbd&fg=000000&s=0...

Hey all, I've just started tensor analysis but do not understand why in contravarient uses 1 and covarient uses 2, could someone please explain these? Perhaps my understanding of the definitions is causing me to misunderstand why its written like this. Any help appreciated.

Homework Statement The problem is f(x) = sin2πx - (1/πsquare)*sinπx and its given Bn sin (nπx) = f(x) Question is find Bn. Homework Equations Bn = 2/L ∫ (sin2πx - (1/πsquare)*sinπx) * sin(nπx/L) where L is 1 The Attempt at a Solution I did [/B] ∫ sin2πx * sin (nπx) - (1/πsquare)*sin...

Homework Statement Homework Equations Momentum = mass x velocity The Attempt at a Solution Answer is A. when mass decreases, speed should increase for momentum to be constant. and when mass increases, velocity decreases. i could understand the graph up the before t2 with this. but at t2...

I will be using /= to mean 'does not equal'. From my textbook: Division Algorithm: Let R be any ring and let f(x) and g(x) be polynomials in R[x]. Assume that f(x) /= 0 and that the leading coefficient of f(x) is a unit in R. then unique determined polynomials q(x) and r(x) exist such that 1)...

I'm curious about time dilation sizes of below 4 situations. Please assume I'm observing the situations far away in zero gravity. And please ignore all SR effects, just focus on GR. http://dishdev.me/data/timedilationq.png Equivalence Principle says acceleration and gravitational fields can...

Hii,i'm new in electrical and much confused bcoz of complicated relation between V,I, nd P. If P = VI = cons. and increasing V,decrease the value of I, but since P is also equal to I×I ×R and r is cons.,so decrease in I will always cause P to decrease which is supposed to remain constant. And i...

I've been trying to understand the major systems for hours. All are ridiculously complicated and seem to make no sense. Wikipedia articles are poorly written and google is having a hard time digging something useful. If any of you guys have any links that do a good job of explaining any system...

[Mentor's note: this post does not use the homework template because it was originally posted in a non-homework forum. It was moved here because it had already received some help.] ---------- Weiping lifts a rock with a weight of 1.0 N through a height of 1.0 m, and then lowers it back...

Hi guys Do electrons move from high to low potential or from low to high potential I think the first one ia right because when electrons are attracted to the negative terminal they have maximum potential energy

Hello, We know that surface integrals come to the form of a surface integral of a scalar function over a surface and a vector field over a surface. First one is \oint F(x,y,z)d{S} and the second one is \oint \vec{F}(x,y,z)\cdot d\vec{S}=\oint \vec{F}(x,y,z)\cdot \vec{n}dS, where n is the unit...

Homework Statement The mathematical complication I'm having comes from Problem 1.9 in Griffiths' Introduction to Quantum Mechanics. I'm just going to provide the mathematics here: The norm squared of the wave function is \ \left|\Psi \right|^{2} = (\frac{2am}{h\pi})^{1/2}...

Homework Statement DC analysis is required for the question in attachment. Vz=6V B=100 Vbe=0.7V Homework Equations The Attempt at a Solution I tried to find the result using the currents that were defined by the transistor. I found a result that was nonsense, the base current...

Hi everyone: I just started to learn special relativity but totally being confused about "velocity", "momentum" and "force". 1. The relativistic momentum is defined by "rest mass * ordinary velocity * gamma". There are 2 kind of explanations. The first one is combining "rest mass * gamma"...

Hello, I have a tricky chain rule question, I think understanding it is more difficult than solving. For the function z=f(x,y) it is given that: f_{y}(0,-3)=-2 and \[f_{x}(0,-3)=3\] so for the function \[g(x,y)=f(2\cdot ln(x+y),x^{4}-3y^{2})\] choose the correct answer: (1)...

Question: A glass half filled with water is kept on a horizontal table in a train. Will the free surface of water remain horizontal as the train starts? If not, which way would it tilt? Attempt: I know this is similar to the 'passenger in a bus' situation discussed in texts. I've identified...

Solve the equation below for D. Assume that matrices A and B are both invertible and that all matrices are equivalently shaped as NxN (e.g., 3x3 ...). Equation: ABDB-1 = I

Hello, I am doing some physics and I end up with this PDE: \frac{\partial q(x,y,t)}{\partial t} = -(x^2 + y^2)q(x,y,t) + ax\frac{\partial q(x,y,t)}{\partial y} where q(x,y,t) is the scalar field to determine and a is a parameter. I need to consider two types of initial conditions...

We all know that 12/25 + 18/30 is not 30/55 yet students are happily told that they got 12 out of 25 in their first maths test and 18 out of 30 in their second maths test giving a total of 30 out of 55 So in this case 12/25 and 18/30 is 30/55 So should we be surprised when students say...

Hi, I have x =(x^2+y^2)^[1/2] I differentiate 1= 1/2 (x^2+y^2)[-1/2] (2x+2yy') So far so good. I try to multiply this out. 1= (2x)/2 (x^2+y^2)[-1/2] + (2yy'/2)(x^2+y^2)[-1/2] I solve for y' y'= 1/{(x (x^2+y^2)[-1/2]} / {y(x^2+y^2)[-1/2] } 1/x (x^2+y^2)[1/2] * 1/y (x^2+y^2)[1/2] The...

Confused on how we go from \frac{1}{^4\sqrt{1 + x}} to \frac{4}{3}(1 + x)^\frac{3}{4} Can someone please show me step-by-step. I need to see the basic steps. Thanks in advance.

I'm working on some MIT OCW for probability theory, and I've come across some confusing notation in the assignmnet. Look at exercise 3 here: http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-436j-fundamentals-of-probability-fall-2008/assignments/MIT6_436JF08_hw01.pdf...

How many linear equations are needed to find the constraints in the polynomial when modelling data that has been found to follow a linear function?" The question seems way too wordy in itself and I have not been able to find anything useful in my textbook or external resources. Can...

Hello, Its been sometime since I touched calculus so some concepts seem to evade me. I understand all the related maths but can't seem to make an intuitive sense of the curl in this case. Green's theorem relates the line integral of a closed curve to the double integral of the curl of the...

I've always found it confusing that light is the only wave that doesn't move through a medium, is it possible that light does move through a medium, and dark matter is the parts of the universe the medium doesn't extend to.

Homework Statement A certain practical dc voltage source can provide a current of 10.5 A when it is (momentarily) short- circuited, and can provide of 30 W to a 20 Ω load. Find the open-circuit voltage Homework Equations V=IR The Attempt at a Solution Well I'm pretty sure that...

I got this question as an example question and I have no clue on how to solve part B Chlorine can be produced by the reaction: 2KMnO4 + 16HCl ->2KCl + 2MnCl2 + 5Cl2 + 8H2O (a)What mass of KMnO4 is required to produce 2.5 L of Cl2 gas measured at STP? For part A I got 7.05 g ( 0.044615...

Homework Statement Suppose a plane flies at a constant groundspeed of 500 miles per hour due east and encounters a 50 mile-per-hour wind from the northwest. Both the airspeed and the compass direction must change to for the plane to maintain its groundspeed and eastward direction. Find the...

This proof makes no sense to me. The theorem to be proved is Theorem 44. {x,y} = {u,v} → (x = u & y = v) V (x = v & y = u) where {x,y} and {u,v} are sets with exactly two members, which can be either sets or individuals. The proof relies on: Theorem 43. z \in {x,y} z = x V z = y...

Hiya! Sam here,...and I'm new. I need help with this online homework problem. To be honeset, I have no idea where to even begin. I've tried the momentum equation where mass times velocity times a proportionality factor gamma, and I think it's the wrong start. Please help?? Question: A skater...

Homework Statement http://grephysics.net/ans/8677/44 Homework Equations p=mv The Attempt at a Solution Can somebody show me the math on why this is true? I feel like in my head if a particle hits the stick in the center of mass instead of at the end it would then make the center of...

Confusing Solid And Plane Angles ! Supplementary Quantities - 1.Solid Angle - Steradian 2.Plane Angle - Radian Doubts - 1.What Is The Use Of Supplementary Quantities ? Physical Quantities Are Used To Measure For Example .. To Measure Length - m Current - ampere Etc... What Can I...