Confusion Definition and 1000 Threads

Homework Statement http://imgur.com/48cLE6q Homework Equations Coulomb's law The Attempt at a Solution I can follow most of this problem, but I am unsure where the constants in front of the trig functions are coming from. Why is it 2cos(135), 1cos(45), 2cos(-45), etc?

Homework Statement A light string is passed over a pulley and two masses m1 and m2 are suspended from the two free ends. The pulley is a uniform circular disc of mass M. Find the linear acceleration of the two masses. Friction may be neglected. Homework Equations I through center of the disc =...

"As you sit in your chair and study your physics (presuming that you do), the force of gravity acts downward upon your body. The reaction force to the force of the Earth pulling you downward is the force of your body pulling the Earth upwards". I read this somewhere just a bit ago and it's...

Can radiation be defined as mass transfer or hear transfer? Like alpha rays and cathode rays involve particles so they could be called as mass transfer and at the same time the transfer energy which is heat energy.

I'm having a lot of confusions in the 3rd law of motion.It says action and reaction forces do not create equilibrium as the forces act upon two different bodies.Okay,I understand that if I want to make a body move I'll have to count the net force that is acting upon it not the force that is...

This may be a matter of me being confused by the definition of heat. However, I view heat as the energy passed between systems of different temperatures. My problem is the following: By the principle of minimum energy/max entropy, in an isolated system (and therefore fixed internal energy)...

Ok, I wasn't sure where to post this, so I posted it here, not sure if it's the best forum for it. Anyway, lately I've tried to explain the mechanism of tides more or less on my own, as an exercise. It's went well, until now. I've tried to explain diurnal and semidiurnal tides, and I came up...

Hi. I'm having trouble solving: 29 - { 5 + 3 [ 8 × ( 10 - √64 ) ] - 50 } My attempt: 29 - { 8 [ 8 × ( 2 ) ] - 50 } = [ 8 × 2 = 16 ] then { 8 × 16 = 128 - 50 = 78 } - 29 = 49 but the calculator says the answer is 126 and I don't know how it arrived at that solution. The textbook doesn't...

I've been looking for a simple exact, gravitational plane wave solution. Working from Wiki's short article on Brinkmann coordinates, I have what appears to be a simple exact solution - but it's significance and interpretation is confusing me a bit. Let's start with the metric: $$g = (y^2 -...

I'm confused about the terminals in the picture above simply because I've seen the exact same thing mean 2 different things in schematics, namely: (1) it is an open circuit with voltage Vi(t) (2) The terminals are connected to some other circuit and thus have a voltage/current source, and the...

I am confused about conformal transformations on Riemannian manifolds. Here's what I have so far. 1. Under a conformal transformation the metric changes by: g' -> Ω2g 2. Under a Weyl transformation the metric changes by: g' -> exp(-2f)g 3. Any 2D Riemann manifold is locally conformally...

Ok. I get that objects seem to fall because of curved spacetime, when they're actually just moving in straight paths. I get the example of ants walking in straight lines on the surface of a sphere, thinking that something attracts them to each other. What I don't get is how the "ants" are...

If Earth was turned into an air-hockey planet, with no friction (or air friction), and I was in New York and I shoved an air hockey puck North, would the hockey puck trace out the same sinusoidal-type path that a satellite/space station does (spending an equal amount of time in the northern and...

Homework Statement high school has 417 students total 186 of total are athletes (play sports) 136 of total are musicians (play music) 74 of total are musicians and athletes. (play music and play sports) a) at which probability does randomly chosen athlete also play music (i.e. be a musician)...

If I would displace a negative one-coulomb charge r meters from a positive charge, Q, the negative charge would gain electric potential energy that would be calculated by summing up all the values of the electric potentials along the line of its displacement, r. (I don't know calculus, but I...

I am reading Maxwell's "a treatise on electricity and magnetism, Volume 2, page 156" about "Ampere's Force Law". I have some confusion in the following pages: My question is of two parts: 1.Equation 20, i.e. ##P=\dfrac{B+C}{2r}## is the outcome of special case (i.e. l=1, m=0, n=0) But in...

Homework Statement car's battery has voltage (E) 11,5 volts and internal resistance of 0,040 ohms. battery's charge is 20 amperehours (20 Ah) How many ignition attempts of the car can be made, when the charge can be allowed to fall to 15 amperehours. One attempt of at engine ignition...

Hi everyone here. I have my question in the following attached pdf file

One of my students asked me the seemingly innocuous question of "how does wind affect the speed of sound?". My immediate thought was that the velocity of the wave would be the vector sum of the velocity of the wind and the velocity of sound waves in still air. However, upon further reflection I...

My teacher posted on his website, Lewis structures of different compounds. One of them were N3- Why isn't there a dipole moment arrow pointing from the central atom to the other Nitrogen? Does the arrow only point from neutral atom to negatively charged atom?

So the moment of inertia or a ring is MR2 I don't understand why. Here is my reasoning Consider this shape (the ball is a point), the moment of inertia is MR2, there I agree but now what happens when you add another point on the other side since I = ΣMR2 then this is 2MR2 What about a...

I am not the best at drawing, I know. If A exerts a force of 200N on B, then by Newton's third law, 200N would be exerted on it. Similarly, if B exerts 100N on A, by Newton's third law, 100N would be exerted on it. Then why wouldn't both accelerate in opposite directions with accelerations equal...

Hi everyone. I'm currently studying waves in physics at the moment but I'm super confused and hoping someone could help me clear up some things. Firstly I'll post what I think it correct (I know it's wrong) and hopefully someone could pick up exactly where I am getting confused. Waves are a...

I have a problem with understanding the nature of collisions and their outcomes. From my understanding, I come to think that when a mass collides with another, both of them should always have equal velocities post-collision. For example, when a mass moving at v1, m1, collides with a mass at...

Okay, so I'm working with the diagrams above. ##i## denotes incident, ##r## reflected, and ##t## transmitted. -We're working in two HIL dielectrics. Incoming and outgoing waves are of form ##Aexp[i(\vec{k}\cdot\vec{r}- \omega t) ##. As I understand it, Maxwell's equations give four boundary...

So 1u = 931.5Mev/c2 = 1.67 10_27 kg . the thing is when i calculate E=mC2 with both units the calculations don't match . i can't understand why .

I'm a little confused on geometric series. My book says that a geometric series is a series of the type: n=1 to ∞, ∑arn-1 If r<1 the series converges to a/(1-r), otherwise the series diverges. So let's say we have a series: n=1 to ∞, ∑An, with An = 1/2n An can be re-written as (1/2)n, which...

In the opening paragraph of section 6.3 Carroll defines a killing horizon to be a null hypersurface Σ where some killing vector field χμ becomes null. Later (on page 247 if you have the book) when distinguishing between static and stationary space times, he says that in a stationary, but not...

Say a girl has brown eyes .she meets with an accident which causes her to undergo an eye transplantation.The donor has blue eyes and the girl gets them.Now does she possesses a blue or brown eye ? So she genetically has brown eyes but phenotypically has blue eyes ? Is it like that? But phenotype...

I'm not sure how magnetic field strenghts and dipoles work. I know that the strenght decreases by 1/r^3, but - isn't magnetic field strenght a constant inherent to the magnet? - if it is not constant, what is? - how is all this related to magnetic damping force?

I have learned that the gravity at the center of the Earth is zero. I guess its because it gets balanced as the force from all the sides are equal in magnitude and opp in direction. But several land forms throughout the world having different masses could cause a distortion which could make an...

An alternative formulation of the second law is that the energy of the system U is minimised if the temperature and entropy of the system are held constant. However, dU= TdS -pdV which means that U is presumably constant if the volume V and the entropy S are kept constant. How then can U...

1. The problem statement, all variables and given/known Two objects move with initial velocity -8.00 m/s xfinal velocity 16.0 m/s xand constant accelerations. (a) The first object has displacement 20.0 m. Find its accelera- tion. (b) The second object travels a total distance of 22.0 m. Find...

We know that the solution of the schroedinger equation for a free particle in position representation is a plane wave: \psi(x)=Ae^{ikx}+Be^{-ikx} which means that the particle has a probability to move either to the left or to the right. "Now let's take the potential step problem. V(x)=0 for...

while solving differential equations, I got a bit confused with chain rule problem. The solution says below yprime = z then y double prime = z (dz/dy) = z prime but I don't understand why the differentiation of z is in that form. Please help...

Hi- Sorry if this is a silly question, but by definition the magnetic flux is given by integral B dot dA. But From Gauss' law for magnetostatics is this not zero around a closed loop? So would that not then imply that the EMF around any closed loop is zero? Obviously I'm missing something, so I...

I'm battled by my thought of interception. The entangled photon between Alice and Bob, suppose the one at Alice's side is already measured to be 1, so the second is heading over to Bob to be 0. Eve gets to it first and measures it to be 0. Knowing its 0, eve prepares a photon of state 0 and...

So the question goes something like this: Now I've already found the solution to the problem, so I don't need any assistance there, and why I'm not posting this in homework help. What I'm having trouble with is visualizing the situation at some instant right before the cat catches the mouse...

We know that internal energy of ideal gas depends only on temperature. Let's say we have 1 mole of ideal gas with pressure P1, volume V1 and temperature T. Let's call this the state 1. Equation of state for ideal gas applies: PV=RT. Now if we expand (or compress gas) isothermally, gas will then...

I have been reading Nakahara's book "Geometry, Topology & Physics" with the aim of teaching myself some differential geometry. Unfortunately I've gotten a little stuck on the notion of a connection and how it relates to the covariant derivative. As I understand it a connection ##\nabla...

Homework Statement Actually, my confusion originated from solving two different problems... 1) A point object of mass 'm' moving horizontally hits the lower end of the uniform thin rod of length 'l' and mass 'm' and sticks to it. The rod is resting on a horizontal, frictionless surface and...

Really wishing I had paid more attention in high school. I assumed that reactive meant that the element either needed to gain or lose electrons causing it to "want" to grab onto another or be grabbed. Sodium being an example. If I am correct with that part, this next part is where I am picking...

I've been trying to figure out why you can't use the average value of a function to determine the volume of a solid of revolution. As an example: Trying to find the volume of a solid of revolution on y=√x from 0 to 1 around the x-axis. The definite integral is 2/3, which divided by one is...

Hi, PF! Recently, while reading chapter 6 of Incropera's Fundamentals of Heat and Mass Transfer I got into a confusion regarding the velocity boundary layer. The book first states that, as the flow becomes more turbulent, the boundary layer gets thicker, as indicated by both figures attached at...

Homework Statement What average net force is required to bring a 1500kg car to rest from a speed of 27.8m/s within a distance of 55m?Homework Equations v^2=vo^2+2ad vf-vo/(time elapsed) The Attempt at a Solution [/B] I know I need to calculate the acceleration first, so immediately I thought...

I have a number of questions on how circuits really function - my class just found itself looking at circuit diagrams and voltages without any explanation of the basics of how circuits actually work. 1) How does the concept of electric potential difference between two points, like with a point...

Entropy has units of kJ/kg K and energy has units of kJ. So my question is if entropy is not conserved how is energy conserved when there is a unit of energy within entropy?

Suppose ##V## is a complex vector space of dimension ##n## and ##T## an operator in it. Furthermore, suppose ##v\in V##. Then I form a list of vectors in ##V##, ##(v,Tv,T^2v,\ldots,T^mv)## where ##m>n##. Due to the last inequality, the vectors in that list must be linearly dependent. This...

On just about every thread concerning the Big Bang, beginner questions are asked which other members consider to be unfounded. Hopefully this thread can serve as a central point to help beginners understand this issue correctly. 1. Where did the Big Bang happen and how far away is Earth from...

Please excuse my ignorance as I request some clarification. I was researching the possible increase in gravity as a body's velocity increases and there was so ambiguity for some were saying that gravity does increase with an increase in relativistic mass while others were denouncing this...