Constant Definition and 1000 Threads

Homework Statement What should be the spring constant k of a spring designed to bring a 1400 kg car to rest from a speed of 28 m/sec so that the occupants undergo a maximum acceleration of 5g’s? I have the solution manual and can see how they did this, but am curious as to why my attempt did...

Hi! While testing my knowledge of analytical mechanics I stumbled across a fallacy that I am unable to resolve. Could you assist me? When you finish integrating a Lagrangian over the time domain ##[t_1,t_2]##, shouldn't its position ##q(t)## and position dot ##\dot{q(t)}## variables take the...

I am curious about a statement that is usually tacked onto the end of a derivation showing enthalpy with constant pressure being equal to the heat into the system. First Law of Thermodynamics \Delta U = Q - W_{by} Define Enthalpy and look at its change: H=U+PV \\ \Delta H = \Delta U +...

Why magnetic constant is specifically 4*pi*10^-7? I can understand other experimental values, for example it would make sense if it was 3.1415*10^-7. But 4*pi is something we can never confirm experimentally since pi has infinitely many digits. So there has to be theoretical reason for us to...

In my textbook it is written that Electric charge on plates of capacitors (without dielectric ) is Q=CV And when dielectric is inserted in the space between plates of capacitors .charge Q remains the same whereas values of C and V change. i.e Q=C'V' is it correct?

My friend and I were discussing this, and google didn't seem to reveal any result. Much like how Bohr's theory managed to derive the Rydberg constant without much effort, has the gravitational constant been found in terms of other quantities yet? It just seems bizarre that Newton proposed a...

I believe what I am attempting to do is not possible but here goes. I want to design a fixed overall length coil which I can manually adjust the pitch on. Optimally one would be able to grab the coil and by twisting it in place would be able to change it's pitch by changing its diameter but not...

Homework Statement Suppose that f:R->R satisfies the inequality ##|\sum\limits_{k=1}^n3^k[f(x+ky)-f(x-ky)]|<=1## for every positive integer k, for all real x, y. Prove that f is a constant function. Homework Equations None The Attempt at a Solution I tried taking f(x)=sinx and then using...

Sorry for the simplicity of the question but I encountered a simple math problem whilst autodidacting myself on classical physics. I seen that a surplus of a specific constant variable "b" was extracted from an integral after a bit of manipulation. ∫xdx was turned into b2∫(x/b)d(x/b) Does the...

What does it mean if a scalar field φ is said to be constant on a surface S? Does φ then have a particular mathematical relationship with S?

Homework Statement (a)Sketch how the contributions change with time (b)For no cosmological constant, how long will this universe exist? (c)How far would a photon travel in this metric? (d)Find particular density ##\rho_E## and scale factor (e)How would this universe evolve?[/B] Homework...

Homework Statement Mass car 1200 kg . power car constant 20kw . Resistance car motion 500N. Car passes point X and Y with speeds 10 m/s ,25 m/s. Car takes 30.5 s to travel from X to Y 1. Find acc of car at x 2.considering work/energy find distance XYHomework EquationsThe Attempt at a Solution

Homework Statement A particle moves on the surface of an inverted cone. The Lagrangian is given by Show that there is a solution of the equations of motion where and take constant values and respectively Homework Equations The equations of motion and are (1) (2) So can be...

Is light's speed constant? The universe is expanding, i think the distant b/w the planets&stars are increasing is that true? is it true then is the time taken to reach sun light to Earth now from past change? if the time is constant then how the speed of light is constant?

Dirac had proposed that Gravitational constant would reduce with time.Why?

I am hoping to recover some of the knowledge of physics I gained in high school that has vanished into the mists of time. Currently, I am being abused on Facebook by a self-proclaimed authority who ridicules my contention that gravitational acceleration is a constant. I get the idea that gravity...

I was wondering why is there a constant that isn't really a constant in mathematics? I am talking about "e", as in exponent e which is the base of the natural logarithm. By definition e = lim (1 + 1/n)^n as n approaches infinity, but doesn't this make e a non-constant since infinity always...

What is the cosmological constant for the Godel metric?

Is there agreement here regarding the relationship between expansion of the universe from its initial conditions, entropy (2nd law), time, (and more tenuously perhaps) "evolution"? I asked a question awhile back that was too specific I think that tried to tie the constant of expansion to the...

I posted this earlier, but I just realized it might have been in the wrong section. Sorry Okay, so consider you have system in which ΔG<0 and ΔS>0. Using Gibbs free energy (ΔG=ΔH-TΔS), you'll know that it will always be negative. As the temperature increases, it will actually become more and...

Homework Statement Distance from planet = 10^14 meters, Radious of the planet = 10^7 meters, mass of the object = 100kg g on the planet's surface = 10 m/s^2, g 10^14 meters away from the planets center = 2.5 m/s^2 Homework Equations Fg=G*m*M/r^2 The Attempt at a Solution I calculated the...

I don't know what to say. sqrt(4) = +/- 2, but constants are fixed. When written sqrt(4), it seems sqrt(4) is a constant, but not in the latter case. Help!

What does the metric look like for constant uniform acceleration, say in the x-direction? ds^2 = g_tt (cdt)^2 + g_xx (dx)^2 g_tt = ? g_xx = ?

It's a combination of centrifugal force and gravity that allows constant acceleration of a rotating object? also is it just coincidence that the most dense objects are near the sun?

Homework Statement Consider a satellite in circular low Mars orbit 300km above the planetary surface. R = 3396km M = 6.419 x 1023kg G = 6.674 x 10-11m3/kg/s2 Find the orbital velocity of the satellite (using the given values, I assume, as there is some inaccuracy in the real-life mass value...

Homework Statement Hello, I'm just curious as to whether I'm going about solving the following problem correctly... Problem Statement: A particle mass m and charge q is in the ground state of a one -dimensional harmonic oscillator, the oscillator frequency is ω_o. An electric field ε_o is...

When modelling the heat transfer through a plate using fouriers equation, what difference would it make if the width and length of the plate were set to a specified value rather than being infinite?

In the book, briefer history of time, hawking says that maxwell's theory of electromagnetism, concluded that speed of light is finite and constant, which made other physicists to give up the idea of absolute time, and think of newer concepts. How did maxwell, through his theories, correctly said...

I've read online that the fine-structure constant (alpha) is at a sort of "goldilocks value" for life generation; if it were 4% lower, stars would not produce carbon or oxygen in their fusion, and if it were greater than 0.1, fusion simply wouldn't occur. These are interesting facts, but can...

I reading book, part about gravity. It is Landau-Lifschiz, "Theory of field". And I trying to understand how to calculate cosmological constant. Re-read part with introduction of cosmological constant several times, still not understood. Let's imagine function of space curvature, without...

Homework Statement (56th Polish Olympiad in Physics, II stage) A photographer has a camera with a lens of focal ##f## with can be set to a value from the interval ##[f_{min}, f_{max}]##. The diameter of the diaphragm is ##d##. The photographer wants to make a photo of a friend so that the...

Homework Statement Given a harmonic oscillator with mass m, and spring constant k, is subject to damping force F= cdx/dt and driven by an external force of the form F[ext]= FoSin(wt). A) Find the steady state solution. B) Find the amplitude and the phase. Homework Equations F=-kx the steady...

I was reading a book about cosmolgy.And there wrotes vacuum energy must be higher than cosmological constant 10100 times to satisfy (It may just the opposite ) observations. Is that true ?

Homework Statement (Not this exactly, but it gets the idea across) I have a square loop of wire with sides L and at t=0, I have the bottom side of the loop right above a uniform magnetic field. So the flux is 0 at t=0, and right when I drop the loop, it is forced downwards at a magnitude...

Homework Statement (Sorry for my bad English) A slippery (frictionless), light horizontal bar rotates about a vertical axis with a constant angular velocity ω. A cylinder with mass m, is initially attatched to a thread with length a and to a spring, which from the beginning has its "natural"...

Homework Statement Most physics problems that involve a falling body assume constant acceleration. How does one account for the changing acceleration if a body is dropped from a very high altitude? Homework Equations With constant acceleration, d = (1/2)at^2 or t = sqrt(2d/a) but a is not...

[Mentor's note: this was originally posted in the Quantum Physics forum, so that is what "this section" means below.] ---------------------------------------------------- I wasn't sure whether to post this question in this section or the general math section, so I just decided to do it here...

Homework Statement when 10 cm3 of a monoprotic acid C3H6O3, with concentration of 7.2g/dm3, was titrated against against 0.05M NaCl, the equivalence point reached when 15.75cm3 (ph8) of NaOH was used. Calculate the acid dissociation constant Ka for C3H6O3. Homework EquationsThe Attempt at a...

Hello! Well, I am in trouble with this question for some time. I am making a simulator with autonomous cars and its movement is done applying constant impulses to the wheel. My question is: if the vehicle is in the intertia state and I start to apply this impulses, the vehicle will assume a...

Consider a holonomic system where I have ##n## not independent variables and one constraint ##f(q1,q2,...,qN,t)=0##. One can rewrite the minimal action principle as: ##\frac{\partial L}{\partial q_i} - \frac{d}{dt} \frac{\partial L}{\partial q'_i} - \lambda \frac{\partial f}{\partial q_i} = 0...

Homework Statement During a tennis serve, the ball goes from rest to approximately 32.3 m/s. The average power generated during the serve is equal to 2672 Watts. If the acceleration is constant during the serve, what is the magnitude of the force acting on the ball? Homework Equations P= F v...

Homework Statement In my physics 12 class, we were given a spring and had to launch it at an angle into a target (the object launched is the spring itself). The target was on the floor level but the spring was launched from above the floor level. I need to find out how far to pull the spring...

for the following 2 examples from: http://www.physicsclassroom.com/class/energy/Lesson-1/Calculating-the-Amount-of-Work-Done-by-Forces A 10-N force is applied to push a block across a frictional surface at constant speed for a displacement of 5.0 m to the right. Would it be more accurate to...

Homework Statement Find the electric potential of a point charge with constant velocity ##v##. Homework Equations $$V(\mathbf{r}, t) = \frac{1}{4\pi\epsilon_0} \int \frac{\rho\left(\mathbf{r}', t - \frac{| \mathbf{r}- \mathbf{r}'| }{c}\right)}{| \mathbf{r}- \mathbf{r}'|}d^3r' $$ The Attempt...

Homework Statement (Sorry for my bad English) A slippery (frictionless), light horizontal bar rotates about a vertical axis with a constant angular velocity ω. A cylinder with mass m, is initially attatched to a thread with length a and to a spring, which from the beginning has its "natural"...

Homework Statement A blackbody photon gas is contained within an evacuated cavity (V = 0.01 m^3). Calculate C_p for the photon gas at T = 1000K Homework Equations C_p - C_v = T(\frac{\partial S} {\partial V}) (\frac{\partial V}{\partial T}) C_v = T(\frac{\partial S} {\partial T}) S =...

Does the mass flow rate differ depending on whether it's after the feedwater heaters or before the turbines or is it just constant throughout the entire system?

This is a two part question and something I think I should know off the top of my head, but I don't, and I can't find a ready answer to it on at least a cursory search. The first part has to do with defining a frequency of a wave in general. I can sit here and tap out a beat on a drum that...

So the Universe expanded very rapidly in its very first moments (inflation). The Universe then slowed down and is speeding up again, and Dark energy is supposed to be responsible for this accelerated expansion. The cosmological constant might as well be dark energy, but why is it still being...

Hi all, this my first forum ever. I'm a self taught physicist. So pardon my ignorance. I pose this question. If speed :s = distance :d ÷ by time :t Then how can we possibly measure our cosmos accurately with a measure of speed aka "Light Speed". The problem I see with this is TIME is a variable...