Constant Definition and 1000 Threads

When the textbook differentiated with respect to time, I see that the middle term is R(dI/dt). Why can't it be I(dR/dt)? When I differentiate, how do I know which letter to differentiate? 3. The Attempt at a Solution 2. Homework Equations 1. Homework Statement

Homework Statement A mass is attached to a spring which is mounted onto a wall. This mass is on a frictionless horizontal surface. You apply a CONSTANT force to the mass and it comes to a stop in 10 cm. My question is, that since the mass comes to a stop in 10 cm then: Force Applied = kx...

Hello everyone, How does Einstein established the equivalence between mass and energy, or in other words what is the fact that proves this.And why the constant is not just C but C square. Why C anyway ??

Homework Statement I'm given a initial and final pressure and temperature of an ideal gas to solve for the work done after it expans in a polytropic process (n=1.2) Homework Equations W = integral of P*dV PV = nRT PV = RT* PV = mRT PV^n = Constant The Attempt at a Solution I get W = integral...

1. Homework Statement A gas (treated as air) powered turbine provides power to a compressor which then sends the compressed air through an intercooler (heat exchanger). Turbine: Gas enters @ 0.03kg/s, 370 degrees Celsius Gas leaves @ 300 degrees Celsius and a "lower pressure" Compressor...

How to find value of integration constant?I know with the help of boundary conditions,but How boundary conditions help in finding integration constant?

Homework Statement Which one of these motions is at constant acceleration? A) A car moving at a constant speed and constant direction. B) A train making stops along its route. C) A moon orbiting a planet. Homework EquationsThe Attempt at a Solution I believe that A is an acceptable answer...

Hy friends I am new here and its my first post. Iwant to ask that a sattalite orbits around Earth with constant velocity.then it has acceleration or not?

Homework Statement In the Principles of Physics book chapter two in checkpoint 2 claims that If velocity of object is zero its a constant velocity.I am confused cause v=0 means there's no motion.Without motion we can't talk about constant velocity.I am confused.(The equation of object is...

In a simple series RC circuit, when t=RC, the voltage across the resistor and capacitor is the same. Why is this physically significant and why do we choose this as the time constant that dictates the cutoff frequency?

1. The scenario If we have a small cuboid volume embedded in a larger dito with periodic boundary conditions, and a wave function that is constant inside the former, while zero everywhere else; what can we then know about the momentum? Homework Equations I. Âψ = Aψ (A being the measured...

Hi, not a homework problem as such, but I am studying introductory quantum physics and having some trouble understanding how applying the rising or lowering operator for angular momentum implies: L+/-|l,m> ∝ |l, m+/-1> Basically, my question is the same as the first part (Q1) as described in...

Hello, Is the speed of light constant at all speeds? So will the speed of light (3 x 10^8 m/s) be the same if a person was traveling at 1000 km/hr and if they were stationary. Thanks

Homework Statement Under what conditions is \left\langle{{\mathbf{x} \cdot \mathbf{p}}}\right\rangle a constant. A proof of the quantum virial theorem starts with the computation of the commutator of \left[{\mathbf{x} \cdot \mathbf{p}},{H}\right] . Using that one can show for Heisenberg...

Homework Statement At what rate would stars have to be producing light (how many photons per second per solar mass start) in order for the energy density of photons in the universe be constant? Assume current values of cosmological parameters. Do it for current time. Homework Equations e =...

Homework Statement I have a lab where I have to use two methods to find the capacitance of printer paper. Homework Equations C = kAeo / d The Attempt at a Solution From these slopes, I got k = .897 for the first type (using changing distance between the plates of the capacitor) for the...

Hey all, was watching my downloads today and saw that my download speed was dropping at such a rate that the eta of the download was almost constant, so I was wondering what negative acceleration would be required for the eta to be constant, if time left is size/speed, speed is first derivative...

If a car is traveling at a constant speed of say, 60MPH, is the acceleration of the car 0, or is it equal to the drag and rolling resistance it's facing?

How can a time constant, in parallel plates, be the original value without changing the capacitor?

Homework Statement A mass 2.74 kg is hung from a spring. The mass is pulled down a short distance and released, it oscillates with a frequency f = 1.972 Hz. What is the spring constant for the spring? Homework Equations f=1/2pi*sqrt(k/m) The Attempt at a Solution 1.972 = 1/2pi*sqrt(k/2.74)...

I've read that drag coefficient depends on the shape of the object but I am confused as to what shape means. Does it mean geometric shape or is area included in that? Say I have one sphere of radius r and keep fluid velocity, density, and viscosity constant and find its drag coefficient. Would...

The question is: If quantum mechanics were detectable in planetary orbits, how much larger than the currently accepted value would Plancks constant need to be? Relevant equations ΔxΔpx ≥ħ/2 p=mv Earth-Sun dist 1.496E11 Earth orbit speed 28,900ms^-1 Earth mass 5.972E24 kg The attempt at a...

The Problem: A 1.80 mol sample of an ideal gas is compressed isothermally from 58.1 L to 15.6 L using a constant external pressure of 2.72 atm . Calculate W: Calculate Q: Calculate ΔU: Attempt at solution: I tried W = P(ΔV) to no effect, W = nRTln[Vf/Vi] to no effect. The online...

Hello all, is there an alternative way of displaying ##\frac{x}{e^{x}-1}## as a trigonometric function, not using the bernoulli-numbers ? Thanks in advance

1:question A weight W is suspended from a rigid support by a hard spring with stiffness constant k . The spring is enclosed in a hard plastic sleeve, which prevents horizontal motion, but allows vertical oscillations. A simple pendulum of length l with a bob of mass m (mg<<W) is suspended from...

Homework Statement the volume density of a body centered cubic lattice is 5.3*10^22 Calculate the lattice constant, effective radius of atom, surface density on 110 plane, and distance between two nearest parallel 110 planes. Homework Equations 4/a^3= volume density 2/sqrt2*a^2 The Attempt at...

Homework Statement A material contains two types of atoms (A and B) in a zincblende structure. Atom A is group V with a hard sphere radius of 2.5 Å. Atom B is group III with a hard sphere radius of 1.6 Å. (a) What is the lattice constant of this material assuming that nearest neighbour atoms...

I have a variable voltage constant current power supply 0-300v at 50mA. Is it possible and if so what would be the simplest way to have a parallel circuit with 0-300v 50mA on one side and 0-300v 50uA on the other? A simple resistor isn't going to work because the supply maintains 50mA. Any help...

Homework Statement Two cars travel towards one another on a 21.0m road, the car traveling to the left has an acceleration a_L=2.4m/s^2 the other car an a_R=1.8m/s^2. What is the distance traveled by the left car up to the meeting point? Homework Equations Left Car...

Homework Statement a) A material is composed of two atoms, A with effecitve radius 2.00 angstroms and B with effective radius 3.10 angstroms. The lattice is a body-centred lattice. b)Enter the volume density of either the A or B atoms in atoms/cm3 Homework Equations .5*sqrt3=(r1+r2) surface...

Homework Statement "A jet plane is cruising at 300 m/s when suddenly the pilot turns the engines up to full throttle. After traveling 4.0 km, the jet is moving with a speed of 400 m/s." Homework Equations "What is the jet's acceleration, assuming it to be a constant acceleration?" The Attempt...

I listened to a lecture the other day that some anomalies in observations compared to theory caused Max Plank to derive his famous Constant.

Homework Statement [/B] 1. Rob throws a baseball upwards at 14.2 m/s. His friend, John, is sitting in a tree 4.5m above Rob. a. Calculate how long it will take to reach John. b. If John misses the ball as it moves upwards, how long will it take to reach John again. Homework Equations...

Homework Statement A railway engine of mass 100 tonnes is attached to a line of trucks of total mass 80 tonnes. Assuming there is no resistance to motion, find the tension in the coupling between the engine and the leading truck when the train: (a) has an acceleration of 0.020 ms-2, (b) is...

I have been studying that velocity = displacement / time. Now what if displacement / time always gives me same value - does it means that object is at rest as displacement is same then the body has not moved at all. So in above graph velocity is constant - ie displacement wrt to time is same...

Hello! me and my friends were discussing a few ideas earlier this week and then we suddenly started talking about Einstein's biggest mistake. I was a bit lost because I am not all that familiar with the Cosmological constant and I was wondering how can probability be applied to that mistake?? I...

I'm trying to determine how exactly gear ratio limits velocity. I know that a high torque configuration is generally regarded as low speed, but my calculations do not seem to support that. Basically, I've written a small problem where we have an input gear with constant torque and an output...

Hello folks, I need some physics help. Some background to get us on the same rails :) I am developing a 2D game in my spare time. Player controls an object (aka spaceship) in open space (no gravitation influence) by selecting a point in space. A constant force which is always pointed at the...

Using an eddy current brake, one would expect the damping constant ##δ## to increase with the current ##I## supplied to the eddy current brake. My question is, why is ##δ## proportional to ##I^2## and not merely ##I##? The magnitude of the eddy current is ##\frac{1}{R}\frac{dΦ}{dt}##, which is...

ZapperZ submitted a new PF Insights post Why Is Acceleration Due to Gravity a Constant? Continue reading the Original PF Insights Post.

If I'm traveling on a spaceship at a constant velocity (say 10000 m/s) towards Mars will I feel weightless, or will I feel nearly weightless because I will still be slightly affected by gravity? I know that when astronauts are in the ISS they feel weightless because they are in a constant...

Hi, I was wondering if there is any need in the theory of relativity for Newton's Gravitational Constant 'G' to remain a fundamental constant. Constant in Coulomb's Law can be expressed in 'c' and 'pi', then why Constant in Newton's Law needs to be a fundamental constant??

Consider the following diagram of a projectile motion (##\hat{\bf i}## and ##\hat{\bf j}## are the unit vectors of the ##x## and ##y##-axis respectively) We know that $$F=ma.\tag1$$ This can be rearranged to $$a=\frac Fm.\tag2$$ So there are actually two accelerations, one with magnitude...

In a car moving at constant acceleration, you travel 250 m between the instants at which the speedometer reads 40 km/h and 80 km/h. How many seconds does it take you to travel the 250 m? What is your acceleration? I have thought of finding the average of 40 km/h and 80 km/h to start the problem...

Suppose we have a system of particles that interact via conservative forces. I wish to prove that ##K+U## is a constant of the system with tensor analysis. Here is my procedure: The Lagrangian is ##L=\frac{1}{2}m_i\dot{ r_i}^2-\Phi## Lagrange's equations ##\frac{d}{dt}(\frac{\partial...

You and your friend are in building four equal-length blocks apart, and you meet for lunch. Friend is 1.2 m/s and you are 1.6 m/s. The restaurant is between the two building and you and your friend will arrive at the same instant if both of you leave the buildings at the same instant. In blocks...

How do we know the speed of light is constant? Is it possible that we only perceive it as constant?

İn some fixed point theory books, I saw an expression...But I didnt understand what this mean...Please can you help me ? " It was important in the proof of banach contraction principle that the contraction constant "h" be strictly less than 1. Than gave us control over the rate of convergence...

Homework Statement What's up guys, I'm stuck on #2 of this worksheet,http://luc.edu/faculty/dslavsk/courses/phys111/homework/phys111-2015hw1.pdf The half - life of C - 14 is 5730 years. Determine the value of its decay constant (and express the answer in appropriate MKS units). 2.The attempt...

Homework Statement From the experiment I did my force was equal to 0.0686N +/- 0.00196N and my x (rubber band stretch) was equal to 0.003m +/-0.002. The question asks to determine the force constant k +/- ∆k. Homework Equations F = kx k = F/x ∆k = |k| ∆x/x +∆y/y The Attempt at a Solution k...