Confused — 400 discussions

I'm confused on how you get the formula v=root(2GM/R²). I know you can use work=forcexdisplacement (W=Fd) so F=W/d. W=½mv² and R=d. Hence, F=½mv²/R Equate that to F=GmM/R² and rearrange to get v=root(2GM/R²). That makes sense as it involves the kinetic energy needed/work done in reaching orbit...

Homework Statement Hello guys, Long problem but I'll drastically shorten it. I've a diatomic ideal gas of N molecules (the 2 atoms are distinct). I must calculate the internal energy and the specific heat for high temperatures. I've got the solution but if I solve it my way in the last step, I...

Homework Statement [/B] Homework Equations There's not much to write here except parallel resistors equation. This is supposed to be a superposition problem. How did he use a source transformation because I have no idea why and where he did the equivalent resistor and why did a current...

Motional EMF is defined as E = -vBL Where B is the magnetic field in Tesla, L is the length in meters and ,v is the velocity. Lets say we have a distance(1m) where half of it(0.5m)the magnetic field is present. So, there is a wire that moves with constant acceleration throughout that whole...

Homework Statement q)a rain drop of mass m is falling vertically through air with steady speed v the rain drop experiences retarding force kv,,k is constant,,acceleration of free fall is g,,k.e of drop is a)mg/k b)m.g^2/2k^2 c)m^3.g^2/k^2 d)m^3.g^2/2k^2 e)m^2.g/k Homework Equations...

Homework Statement A fire hose for use in urban areas must be able to shoot a stream of water to a maximum height of 34m . The water leaves the hose at ground level in a circular stream 3.0cm in diameter. What minimum power is required to create such a stream of water? Every cubic meter of...

I need to prove that $$std(x+c) = std(x)$$ I have been trying to use the properties of the mean such as $$mean(x+c) = mean(x) + c$$ I am confused on the following property of the mean, is this statement correct? $$\sum\limits_{i=1}^{i=N}(x_i - mean(\{x\}))^2 = mean(\{x\}) \\$$ If that is...

As a senior in High School in Chicago, I was planning on pursuing a Masters Degree in physics at University of Illinois at Urbana Champaign. That being said I had a few questions about the career (I don't know any Physicists personally to ask): 1. How easy is it to find a job with a Bachelor of...

Plane wave equation: $$\psi(t) = \psi_0e^{i(\vec{k}\cdot\vec{r}-\omega t)}$$ The part that makes the domain of \psi(t_i) a plane is the k dot r part. I'm reading a book that takes this term and imposes the following condition: $$\vec{k}\cdot\vec{r}=Const.$$ which, i understand its...

Ok, so I got this question on an exam some time ago and I still don't understand why I didn't get it (I can't remember the exact question, but this is very similar): "A lottery winning amount is determined in the following manner: first a die is thrown. If the result is 1 or 2, the lottery...

Let me say from the beginning I'm not talking about the non-coordinate unit vectors for polar coordinates. I'm talking about basis vectors. Let me just ask it as boldly as possible: how does one use these basis vectors in order to describe a vector? I know they are different at every point, so...

I'm studying for my college's physics placement and I'm frustrated because I don't get the solution to problem 1d. Homework Statement The problem is here: http://ocw.edu.ht/courses/physics/8-01-physics-i-classical-mechanics-fall-1999/exams/exam_2.pdf Solution manual is here...

PLz find the attached image. Each link weight is given. the 50 kg weight with link rotates about the red hinge point. angle is as shown. please help me out its urgent. need to calculate the torque about the red hinge point.

This is going to be a really dumb question, but somehow it's not really clicking. I read somewhere that: \int_{a}^{x} f(t)\,dt = F(x) - F(a) But, this is also true: F(x) = \int_{a}^{x} f(t)\,dt. Does this imply that F(x) = F(x) - F(a)? For example, at a random number, c,: F(c) =...

Hi. I am confused about the following problems. Any help would be appreciated. Thanks 1. I don't understand what ψ (r)= <r|ψ> means. What is the difference between the wavefunction ψ and the ket |ψ> ? 2. A similar equation is ψ (p) = <p|ψ>. Is this ket |ψ> the same as the one above or is...

Sketch the region bounded by the line y = 2 and the graph of $$y = sec^2(3x)$$ for $$ \frac{-\pi}{6} < x < \frac{\pi}{6}$$ Very very confused on this problem... So here is what I set up.. Top function - bottom function $$\int ^{\pi/6}_{-\pi/6} 2 - \sec^2(3x) dx$$ so I split the integrals in...

I think the first thing that is confusing me is the terminology. There are too many similar terms (e.g. probability measure, probability distribution, probability density function, probability mass function) What are the general concepts and what are the instances of those concepts? Like, are...

Hi, I am trying to learn some stuff about percolation, specifically what Menshikov's theorem is about. On wiki http://en.wikipedia.org/wiki/Percolation_theory it says: "when p<pc, the probability that a specific point (for example, the origin) is contained in an open cluster of size r...

Hi I'm trying to integrate the following q_m = -D A \frac{dc}{dx} where A = 4 \pi r^2 Yes, a sphere.My supplied literature simplifies to q_m = -D 2 \pi r L \frac{dc}{dr} when A = 2 \pi r L Integrating to \int_{r1}^{r2} q_m \frac{dr}{r} = - \int_{c1}^{c2} 2 \pi L D dc Integrated to q_m ln...

I'm a bit of a non-classical physics newbie here, so let me check my (rudimentary) understanding of some things first. In quantum physics, there are the leptons, quarks, and bosons. All particles are excitations of a field. Bosons in particular are the fields that mediate different kinds of...

I am a high-school student. My Physics's teacher is not good,so I am here. Please anyone explain me "What is volt", so that I will have no confusion with Volt. I will be thankful to you if you clear my confusion.

My professor stated the following: "Dividing in pieces is called 'quantiles'. In almost all cases quartiles are used, where n=4. We divide it into four equal pieces and we are going to check where the margin values are. Pay close attention: if I split my data into 4 equal pieces, I will have...

I'm a freshmen college student pursuing a chemical engineering degree. I have many ideas that I want to create ranging from food processing, recreating the future of human performance equipment, ocean discovery, computer programs, and more. Will majoring in chemical engineering be best suited...

Homework Statement Is {(1; 1; 0);(0; 0; 2);(0; 0; 1);(1; 2; 3)} a spanning set for R3The Attempt at a SolutionThis is supposed to be easy but the answer sheet might be wrong. The answer I have says it is and then proceed to say that (0;0;2) is linearly independent. But it isn't because...

Homework Statement A uniform plank of length l = 6m and mass M= 90kg rests on sawhorses separated by D = 1.5m and equidistant from the center of the plank. Cousin Throckmorton wants to stand on the right-hand end of the plank. If the plank is to remain at rest, how massive can...

Dear all, Please I need your help and suggestions I contacted a professor for a PhD program in electrical engineering. First, he asked me to send him some documents (CV, transcripts,...etc). Then, he told me to apply for the university. Unfortunately, my application has been rejected...

I'm getting myself all confused with complex logarithms. I'll try to explain why. One identity with complex logarithms is ln(z^c)=cln(z)+2πik, with k an integer. This is, of course, a more general case of ln(e^c)=c+2πik, but it doesn't always work the same! Let's say we are evaluating ln(e^i)...

I am havingA LOT of trouble with self-inductance and have spent 10+ hours watching videos on youtube, and I'm still getting nowhere. From what I understand: self inductance = the ability of a thing (not sure what) to resist the change in voltage (and thereby causing current to change more...

Homework Statement So I was looking at this site reading up again on Gauss's Law and was a tad confused http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elecyl.html 1st thing on the page... Homework Equations The Attempt at a Solution It states that the electric flux will just be the...

Why is it that when you drop something on a spring, that item dropped on the spring does not bounce back up to where you dropped it from?

I came across this problem and I'm wondering if anyone can tell me what it means/how to do it: "Given the formula below to model, what is the expected value of rolling two dice simultaneously? $$E(X)= \sum_{i=1}^{\infty}x_i f(x_i)."$$ I've never seen this notation before; how does it work?

In my previous two math classes I'd get the answer wrong if I put the number first then the variable as my answer. Now in this class this way of doing it is wrong. I'm seriously confused now. For instance the last two classes said that it was standard practice to write an answer like: 3x+4. This...

Homework Statement ∫Fdr Over C where C is the cirlce (x-3)^2+ (y+4)^2=4 F=<y-cosy, xsiny> Homework Equations The Attempt at a Solution So I applied Green's theorem and converted to polar and ended up with -4π, it should be positive. The orientation confused me since day one...

Hello, I have the problem statement attached in the thumbnail. I am confused about this question. I looked at the solution manual, and they are saying that the pressure at states 3 and 4 are the same, as well as at states 1 and 2. I don't see how this is. Looking at the carnot cycle PV...

I am very confused on these questions...help please :) stuff in () is what I think the answer is but am not sure. A 100 kg cart and a 200 kg cart move toward each other. The 100 kg cart initially moves at +5 m/s while the 200 kg cart moves at -10 m/s. 1. What is impulse in terms of...

Homework Statement http://postimg.org/image/mzdo4kp7b/ wouldn't the initial angular speed of 50rad/s cause some rotation about the axis at B (so shouldn't the FBD include a torque about B?) http://postimg.org/image/nad9b9rqn/ And in this question, I don't know what Mz is. Is it...

Homework Statement For example in my notes in class the prof went over an example with the following null and alternative hypothesis: I feel like you can switch them around but I am not too sure. I have been trying to figure out when to use greater than or less than for the null...

So I made a banjo for my project and now I need to do the calculations. Well since its a string instrument I have to find the frequencies of the first four harmonics, I already have the fundamental frequency. Is it fine to use: fn = nf1 Not sure because I thought that was for open end air...

Homework Statement Here is a slide in my notes: I am kind of confused about mean and standard deviation. So in my notes it says X1 to Xn are independent measurements. Then it says each independent measurement has a mean μ. But how is this possible, if they are independent measurements (in...

x(n)=exp(i(x*n+theta1)) +exp(i(y*n+theta2)) x and y are constants , theta1, theta2 are uniform random on [0,2*pi] R(f) =E[{ exp(i(x*n+theta1)) +exp(i(y*n+theta2)) }exp(-i(x*(n-f)+theta1)) +exp(-i(y*(n-f)+theta2)) }] = 4 products 2 of which will be similar but with the opposite constants...

Hello! This is my second thread in here. I'm just finished my high school and waiting for the results to get admission in an undergrad physics program. I was confused about career guidance and academic guidance feel free to move my thread if I'm in the wrong place I was wondering about major...

Okay so I'm working on this problem $$\int \frac{x^2}{\sqrt{4 - x^2}} \, dx$$ I do a substitution and set $$x={\sqrt{4}}sinu$$ I get to this step fine $$\int 4sin(u)^2$$ I know that u = arcsin(x/2) so I don't see why I can't just substitute in u into sin(u)? I tried this and I got $$\int...

Hi. When trying to derive the equation for voltage across a discharging capacitor in series with a resistor using Kirchhoff's laws, I got stuck. My attempt was that the voltage gain across the capacitor should equal the voltage drop across the resistor, therefore q(t)/C = i(t)*R, or q(t) -...

do negative charges in electric fields of positive charges have negative electrostatic potential energy? am I write in thinking they can't be at negative potential (V) because potential is a property of the field and has nothing to do with the charge in the field (like potential energy does)...

Confused -- nucleosynthesis of carbon May I ask a question please! I read that nucleosynthesis of carbon was rapid because its one of the excited state energies was only a little higher than the total energy of Be and He. So, the required energy could be obtained through the kinetic energy of...

I need help in understanding back emf, I'm a bit confused here. Example(for understanding): Let's assume we have a 12 V DC motor, that draws 20Amps when it starts, as it reaches maximum speeds, current drops due to back emf, let's assume the resistance is 0.6 ohms, and b.emf = 10V...

I have a question which asks me to estimate the color of a compound in white light. I can easily get the wavelength (hc/dE) as 460nm, which agrees with the book. Looking at a spectrum list that would seem to fall in the blue range, but the book is saying it would be orange because blue is...

Suppose we have $$\int \frac{4}{x^2 + 4} $$ So I understand the first thing we would so is bring the constant out and do u substitution but what I don't understand is how we can make the substitution u = $$\frac{x}{2}$$ when there clearly is no $$\frac{x}{2}$$ in the problem. I also understand...

It is known that the vector in polar coordinate system can be expressed as \mathbf{r}=r\hat{r}. In this formula, we don't see \hat{\theta} appear. But after the derivation yielding speed, \mathbf{v}=\dot{r}\hat{r}+r\dot{\theta}\hat{\theta}. Where does theta come from? And how to define its...

My father's thinking of buying a new car and I'm trying to do research online to help him make the right choice. The issue is that I can't find any research whatsoever. All I get are subjective reviews (which seem to be just marketing ads) and anecdotes. I can't find objective information on...