Confusion Definition and 1000 Threads

Hi. Consider the basic eq for a falling body with air resistance dv/dt=g-kv/m I don't understand air resistance as a force, since it seems irreconcilable to the force equation F=ma. How is a force a function of velocity? I am also not sure how this equation makes sense in terms of...

I am right now studying Rigid Body dynamics.. I have some doubts regarding Dynamics... 1) When a body is rotating as well as translating...we say that every particle of the ..lets say ROD is moving with a resultant velocity = Vcm ( translational velocity of COM) + ω.R (where R is the...

i don't know in which section it belongs, so i am putting it here... according to various theories proposed by various researchers, time travel depends on the speed of light. as far as i have read/heard - i) anything traveling faster than the speed of light moves back in time. ii) anything...

Please can anyone help me?I'm confused here. If I'm following unit of force as Newton, and length as mm; and stress as MPa,then for a consistent system of units (see link below); http://www.dynasupport.com/howtos/general/consistent-units/ what should be the unit for: 1)density 2) rotation

I'm confused by the fact there's nothing in the feedback loop here http://img706.imageshack.us/img706/6075/feedbackloop.jpg For instance, if I had "H1" in the feedback loop I'd do C/R = (Gcs x Gps) / (1+H1) But since I don't have H1... is it simply C/R = (Gcs x Gps) / 1 = Gcs...

Hi :) So I'm learning about lateral inversion in plane mirrors and it's a bit confusing. I think of it like this:- Suppose you had a clone of your self who is standing next to you and facing the same direction. He walks a few steps forward and then turns to face you. When he turns to face...

Hello everyone, I have some conceptual issues with aforementioned definitions. How is exactly multiplicative inverse defined? Say, for a rational, nonzero number a/b, its reciprocal is b/a. Is there a certain operation that transforms a/b to b/a? Also, the notation for multiplicative...

e^(3+2logx) = (3x-2)*e^3 I can get down to this point: e^(logx^2)=3x-2 I have checked the solution in the book, and the steps. Turns out it simplifies to x^2 -3x +2=0. The problem is I can't figure out how I pass from e^(logx^2) to x^2, because as far as I know logx isn't the same as lnx...

http://www.flickr.com/photos/53512951@N06/8229416013/in/photostream/ With regards to the circuit in the image linked above, I have been told to start in the bottom left hand corner and then work clockwise around the circuit, adding up all the voltages to see if they follow the KVL principle...

I have been working through Spivak's fine book, but the part about differential forms and tangent spaces has left me confused. In particular, Spivak defines the Tangent Space \mathbb R^n_p of \mathbb R^n at the point p as the set of tuples (p,x),x\in\mathbb R^n. Afterwards, Vector fields are...

I'm doing coursework on a circuit experiment we performed in class. I'm pretty sure the results are wrong or flawed, but we were testing the effect of increasing the length of wire on the resistance. I had a voltmeter about the wire, a cell, an ammeter, and completed the circuit by attaching the...

I am reading Griffiths and I am having trouble interpreting the results of measuring the x component of spin on a spin-up particle. If you have a spin up particle, my understanding is that it is assumed to be up in the preferred axis, z. I would think that measuring its x component should...

Homework Statement As part of your daily workout, you lie on your back and push with your feet against a platform attached to two stiff springs arranged side by side so that they are parallel to each other. When you push the platform, you compress the springs. You do 80.0 J of work when...

There is a statement in my book i can't really understand. "To stretch a spring, we must do work. We apply equal and opposite forces to the ends of a spring and gradually increase the forces. We hold the left end stationary, so the force we apply at this end does no work.The force at the moving...

Hello, I've been trying to internally conceptualize as much of physics as I could, and doing so I realized that something I thought I understood at first does not actually make any sense in my head anymore. And since it doesn't, I'm afraid that I might have misunderstood a lot of other concepts...

Homework Statement Determine how much distilled water must be added to 250 ml of a 1.5 M solution of Na2CO3 to dilute it to a concentraion of 0.5 M. Homework Equations c1v1=c2v2 The Attempt at a Solution I'm having trouble understanding how to identify c1,v1,c2, and v2, especially since every...

According to Wikipedia: The part I don't understand is why all rays that are sagittal rays that are not the chief/principal rays must be skew. Do they just mean all other rays originating from the same object point must be skew? Because that makes sense. Are these things always discussed...

Let there be an obj. which is made to fall from a certain height in a gravitaitonal field. where a= 10 metre per second squared Say it falls for 1 second. v(final velocity)= 10 metre per second. How much distance does it cover in that 1 second? distance = speed x time = avg...

Hi, I'm reading a book and one of the questions asks: how much force is required to give an object weighing 3000lb an acceleration of 12ft/sec2? I calculated this as F=3000x12=36,000pdl. The answer given is "1125 force" (36,000/32). Why is this? Why isn't it just 36,000pdl?

Fission/Fusion reactions confusion help please Homework Statement http://www.xtremepapers.com/papers/CIE/Cambridge%20International%20A%20and%20AS%20Level/Physics%20%289702%29/9702_s03_qp_4.pdf number 6...

Hi, this is not a homework problem, i just have a hard time following the sequence of this In the book , it shows a couple examples (=== is the triple equal sign) 1) 26=19+7===3+7===10(mod8) 2) 15=19-4===3-4=-1(mod8) 3)38 = 19*2===3*2=6(mod8) 4) 7===2(mod5), 343=7^3===2^3=8(mod5) I...

Hi. Can you clarify for me the equation for g-force below: F= ma + mg I got this equation from my lecturer. He asked the class to determine how was the formula above formulated. But this is not a homework. Is the equation above true for g-force? If it's true, how does...

I was reviewing the first few chapters of Weinberg VolI and found a hole in my understanding in page 112, where he tried to show in the asymptotic past t=-\infty, the in states coincide with a free state. In particular, he argued the integral \int...

We have that \int^{1}_{0}\frac{1}{\sqrt{1-x^{2}}}=lim_{\stackrel{}{t \rightarrow 0^{+}}}\int^{1}_{t}\frac{1}{\sqrt{1-x^{2}}}=lim_{\stackrel{}{t \rightarrow 0^{+}}}[arcsin(x)]^{1}_{t}=\frac{\pi}{2} However, I think \int^{1}_{0}\frac{1}{\sqrt{1-x^{2}}} should equal to lim_{\stackrel{}{t...

My question about this excercise is the 80+20 part in the denominator. Why and when do I do that? I tried doing it but got the wrong answer

In the following link http://en.wikipedia.org/wiki/File:Silicon-tetrafluoride-2D-dimensions.png the bonds are represented pictorially in different ways(like the black triangle). Do these just show the physical structure of the bonds or do they show the different types of bonds?

1.The Question The function f(x)= x2/x if (x≠0) 0 if(x=0) The Attempt at a SolutionI thought this had a removable...

If we set c=G=1, then c=1 leads to L=1/T , the G=1 means that M=L^3/T^2 and combining the two means that M=L=1/T so far so good. But say if I also want \hbar=1 this seems to imply M=T/L^2 but combining this with c=1 which gave the L=1/T now suggests that M=1/L=T . Which seems...

Let g(t) = f(tx, ty). Using the chain rule, we get g'(t) = (\frac{\partial f}{\partial x})(tx, ty) * x + (\frac{\partial f}{\partial y})(tx, ty) * y this was actually part of a proof and what i don't understand is that why didn't they write (\frac{\partial f}{\partial (tx)}) and...

Hi, I am doing a geophysics assignment and had some confusion. Basically I want to know why oceanic crust is so much thinner than continental crust. My friend has told me it's because there is less weight on top of it because the ocean water is not very dense, causing the mantle to rise up...

how do you know when to use dB= 20log(ratio of input/output quantities) or dB=10log(ratio of output and inout). voltage seems to be 20, power seems to be 10... but how about when doing Fourier transforms and you want to find out 3dB of maximum, for example? thanks

Greetings everyone, I am taking a course on elementary condensed matter physics and our textbook is "Introduction to Solid State Physics" by Charles Kittel. I have read the crystal structure from 4 books; however, I am still confused about the definitions such as unit cell, primitive vector and...

Homework Statement There are two circuits I don't entirely understand. I am also new to calculations with complex numbers and when to and when not to use them, so be easy on me. Anyways, the point is to find out what the different meters are showing, when you are given the initial voltage and...

Homework Statement Upton Chuck is riding the Giant Drop at Great America. If Upton free falls for 2.6 seconds, what will be his final velocity and how far will he fall? Homework Equations The Attempt at a Solution Finding V(final)= Vf-Vi = at ---> Vf = (-9.81)(2.6) = 25.5 The...

http://en.wikipedia.org/wiki/File:Doubleslit.gif As shown in the link, diffraction is shown in the form of these kind of longitudinal waves. The diffraction pattern explains the wave interference pattern observed in the double slit experiment. However in the case of the delayed choice double...

Hey there, I'm in a math class and we're covering some applications to physics and although I completely understand the math behind it and am getting the correct answers, I'm a little iffy on how some of the units work. Would anyone be kind enough to tell me whether or not my thought process...

So I have a 10 metre cantilever with a pin in the middle There is a roller at the end and a UDL of 10 kN / m acting across. Drawing the BMD is confusing me. By my calculations; there should be a 50 kN load acting at the fixed end and roller. Hence shape of the shear force diagram would be...

Hello, everybody. I'm reading through my EE textbook and I'm having some confusion about when to combine resistors in series. The following figure is in my book: I see that they combine the parallel resistors of 6Ω and 3Ω to make the equivalent circuit shown in 2.42b. What I'm confused...

Homework Statement A car moves east at 18 m/s for 5 minutes. What its displacement? It says that the answer to this question from my teacher is: 5400 m. Homework Equations → → X= v *t The Attempt at a Solution → V= 18 m/s [E] t= 5 min. → → → X= v *t =...

Hi all, I need help with a paragraph of my book that I don't understand. It says: "the map sending all of ℝ^n into a single point of ℝ^m is an example showing that a continuous map need not send open sets into open sets". My confusion arising because I can't figure out how this map can be...

Homework Statement I will use an example to showcase my confusion: Suppose a person watches show A 2/3 of the time, show B 1/2 of the time, and both show A and show B 1/3 of the time. For a randomly selected day, what is the probability that the person watches only show A? For a randomly...

http://examsolutions.co.uk/a-level-maths-papers/Edexcel/Mechanics/Mechanics-M2/2010-June/paper.php Question 3) part a) I got the answer to be 2.5 which is correct part b) I don't really get how to do this, I understand as a new particle is being added which is the same mass of the...

Hi everyone, I'm having a little confusion here: I measured a value which is 0.27 nN/nm and I converted it's value as 0.27 N/m. Is this correct or should it be 0.27 nN/nm = 0.27*10^9 N/m Thanks for your help

Hi all, I have a very basic doubt. If we have an amplifier with voltage gain A = Vo/Vi , where Vo is output and Vi is input voltages and Ap = Po/Pi which is power gain. Ap = Po/Pi = Vo^2/Vi^2 = (Vo/Vi)^2 In decibels powergain = 10 log (Po/Pi) = 20 log (Vo/Vi). In most tech...

Hello, I just started basic mechanics and what seems to mess with me is this: take a 1kg cube in a string, with how much force do you need to push it to give it the even speed of 2M/S, In the book it says F1-F2=0, so 9,8N=F2, so you have to push it upwards with 9,8 Newtons... but how the hell...

Hi, I am having some confusion regarding pull down resistors. In the schematic I have a 100k pulldown resistor. P1 is the output port and the nOE(OE bar) is the input to a buffer. What is confusing me is if the P1 input is high impedance then the nOE should go high, but when the P1 pin...

Hi all, I'm having trouble with the power required formula for steady level flight. Here's the formula: Preq = 4/3*W*sqrt(W/S*2/ρ*sqrt(3*CD0/(π*ε*A))) I'm using this for a small indoor RC fixed wing. The values I'm using are as follows: Weight, W = 0.3924N Wing Area, S = 0.073 m^2 Density, ρ...

Homework Statement A research submarine has a 40.0cm -diameter window 8.70cm thick. The manufacturer says the window can withstand forces up to 1.20×10^6N . What is the submarine's maximum safe depth? Homework Equations P= atmosheric pressure + ρg(depth) Pressure = Force/crossectional...

Hi, I've very recently begun physics self-teaching as I used to find it boring and thus avoided it as a subject but now find it increasingly interesting. Nevertheless, I'm having some problems regarding questions on Newton's First Law. One of the questions in the book I'm using says the...

Hi, I just finished class and my professor was writing some of Newton's Laws on the board and derived some equations. We ended up with: V(Δt)=FΔt (this is for velocity in first inertial frame V(2Δt)=2FΔt (this is for velocity in second inertial frame Then he went and got the position in...