Per Definition and 565 Threads

Homework Statement You are in a car that is on the top of a steep 500 meter high hill. You are stepping of the brakes so your car is not moving. How much energy per second( power) must be expended to keep the car stationary Homework Equations The Attempt at a Solution

I am reading Aschroft and Mermin and I came across the probability per unit time I have trouble understanding the concept as it is. But they do try to explain. They say that the probability that an electron will experience a collision in an ifinetismal time, dt, is just dt/τ. From this i...

Homework Statement Cold-roiled steel of high silicon content enables the designer to use higher operating flux densities with lower loss per kg. The higher flux density reduces the weight per kVA. Can anyone explain how & why does weight/KVA depends on flux density Homework Equations...

Average Cost. A manufacturer has determined that the total cost $C$ of operating a factory is $C=0.5x^2+15x+5000$ where $x$ is the number of units produced. At what level of production will the average cost per unit be minimized? (The average cost per unit is $\frac{C}{x}$) taking C' and...

Hi all, Homework Statement The motor driving a large grindstone is switched off when a rotational speed of 360 rpm has been achieved. After 15s the speed has decreased to 210rpm. If the angular deceleration remains constant, how many additional revolutions does the stone make before coming to...

Nitrogen dioxide reacts with carbon monoxide by the overall equation: NO2(g) + CO(g) ----> NO(g)+ CO2(g) At a particular temperature, the reaction is second order In NO2 and zero order in CO. The rate constant is 0.515 L/(mol*s). How much heat energy evolves per second initially from 3.50...

I'm trying to find out: -Mass (g) of acetic acid per liter of vinegar and -Mass (g) of solution per liter of vinegar I thought mass (g) of solution meant how much acetic acid but apparently not? what does it mean and how do I calculate it? Thanks :)

I've seen this letter circulating some astrophys blogs recently. Maybe some of you have seen it as well. http://jjcharfman.tumblr.com/post/33151387354/a-motivational-correspondance Essentially, a R1 astrophys department tells its grad students that working less than 60 hours per week is...

How do you calculate cost per unit of electricity over a certain time that a generator produces?

If you had to confirm that gravity equals approximately 9.8 metres per second would you take an object and drop it from different heights. Would you then take the time and displacement and work out velocity and then use that to work out acceleration?? EDIT: In this example there is no air...

Help please...Transmission line parameters in per unit hello there I'm trying to work on a program that converts electrical quantities of transmission line ( R , L , and C ) into per unit system using Matlab the thing is that I'm finding difficulties with the formulas , how I can obtain...

Homework Statement Find the binding energy per nucleon of 238 92 U in MeV Homework Equations ΔM= ideal mass - atomic mass Ebind= ΔM * 931.5 The Attempt at a Solution first i found the diference in mass from ideal weight and atomich weight which is 1.98499. then i multiplied...

Homework Statement A heat engine operating between freezing and boling points of water takes 20 cycles to raise a mass of 1000kg through a height of 3m. Calculate the minimum energy per cycle that must be extracted from the hot reservoir in order to achieve this. Homework Equations...

Hello all, My name is Yusif Nurizade; long time lurker, first time poster. I am taking a summer class which is going at a rather quick pace and I could really use some help with the following problem: A total of 11 different gifts are to be distributed among 15 children. How many...

Recently I saw an article about sled dogs burning 10,000 calories in a day. Even when adjusted for mass, this is significantly more energy than a human athlete might use. This got me thinking: how much energy do bacteria use in a day? Trees? Fungi? Other animals? I can think of lots of...

I am reading a book called advanced physics, which is very good I may add. there is a question in it as follows; The second is defined as 9,192,631,770 periods of radiation from a caesium-133 atom, The metere is defined as the distance traveled by light in 1/299792458 of a second. How many...

I was reading a link i found here on physicsforums called "The relativistic rocket". There was lots of calculations of the required fuel for certain distances and such. However, I understand that time→0 when our velocity v→c. And that will mean we travel a larger distance for a shorter...

If at the big bang, space and time began, would time not travel at a certain rate? Such as, light travels at 299792458m/sec. The solar system has been here for some 5 billion years and we are looking into outerspace at light that has taken 5 billion years to reach us. Would that not mean that...

Homework Statement Starting with: G = \frac{I}{V}= \frac{-\int_{s}\sigma\mathbf{E}\cdot d\boldsymbol{s}}{-\int_{l}\boldsymbol{E}\cdot d\boldsymbol{l}} Derive the conductance per unit length, G', of a coaxial cable by assuming a line charge of \rho_{l} on the center conductor...

You can blame Eddington for this one. I'm a retired electronics guy who now has time to read physics history and recent research also and am totally curious about the nature and most basic definitions of light photons. Eddington mentions in one of his essays in the '20's about "a meters...

So basically, I feel that I have kind of made a mistake in my scheduling strategy thus far, and I'm wondering if anyone else is in the same boat. My plan was to get all of my gen eds (9 cr social/behavioral & 9 cr humanities/fine arts) out of the way as soon as possible so that I could focus on...

1) I'm not sure how to solve this question A 20MVA induction motor connected at 13.8kV draws a load current of 1.0 p.u, 0.85 power factor lag. Calculate the rated load current in Amps and the real power and reactive power drawn by the motor. Express these quantities in per unit form using...

Homework Statement Two parallel whires, separated by a distance D (midpoint distance), are charged with a current density L (each whire has a radius R). If the whires have the potential +/- X Volts, what is the force per unit length between them? Homework Equations B = μ0*I /(2πr) is...

In 2008 the real GDP per hour worked was $45.70? I don't think this means that the average person was making $45.70... Here is that graph that contains this data: http://dl.dropbox.com/u/64325990/ECON%20102/Capture.PNG Could someone please explain the difference?

I'm interested in the theoretical minimum number, so like the extruded buckyball ball? I'm trying to work out if there are enough carbon atoms in a 'piece of paper' to reach the moon. :) Which brings me to the next question : how many carbon atoms are there in a piece of paper? Or...

Homework Statement I don't know if this is a physics problem per se but its from physics class. So we were supposed to pick out a solar panel and figure out what is the cost per unit of energy for this form of solar energy? I know where supposed to use the data sheet for the panel that we...

The SABRE engine, currently being developed by a company in Oxfordshire, England, is a single stage to orbit, experimental hybrid air-breathing/LOX rocket engine with a rather fascinating heat exchanger that pre-cools the air before entering the combustor. What fascinated me the most about this...

In the 1980s, an average of 121.95 workers died on the job each week. Give estimates of the following quantities: a.) the proportion of weeks having 130 deaths or more; b.) the proportion of weeks having 100 deaths or less. Explain your reasoning. Procedure I'm not sure, how to start...

Homework Statement Ok so using the standard equation v = Sqrt(T/Mu) I want to find Mu as a gradient for the first fundamental. I've made it into F x lambda = sqrt(T/Mu) Then f x 2l = sqrt(T/Mu) Then f= sqrt(T/4l^2 Mu) As I'm having the tension held by a mass suspended over a pulley. f=...

This is not homework, but I'm developing a new machine and doing my own research as a mechatronical engineer. I'm trying to calculate the maximum volume of Helium gas that can be ionized into plasma if I apply a power of 1 watt, where the voltage is 1000 volt and the current is 0,1mA. DATA...

Wow, what a Project: Square Kilometer Array This thread is unique, last one was written in 2007 concerning the "Square Kilometer Array". It looks like requirements will push new developments in hardware and software technologies to handle an exobyte of data per day. One half an exobyte of...

Homework Statement Air passes over an electrical heater at a steady rate of 2500cm^3 per second. The inlet temperature of the air is 20^oC ( 20 degrees celcius ) and the steady outlet temperature is 40^0C ( 40 degrees celcius) a) What heat is absorbed by air passing over the heater in 2...

Dear all, My aim is to get the density of states (DOS) per unit area for monolayer (bilayer) graphene. I have done this using mathematica. I have set a sampling k grid with 22500 points and computed the expression: DOS=(1/Nk)*Ʃ δ(E-Ek) where the sum is over the k points in the reciprocal...

Homework Statement Sinusoidal driving force driving a damped oscillator (mass = m). Natural frequency is assumed to equal the drive frequency = w Time has elapsed to the point any transients have dissipated. Show that the energy dissipated by the damping force [F=-bv] during one cycle is...

So I left a thread of posts about this new coax I had made, trying to understand its electrical characteristics such as velocity factor and so on... Then I had an occasion to exchange emails with the MFG asking what the capacitance was per foot. The answer was something like 30pF per foot...

How do you determine the number of conductors per phase? From my understand, the full load amperage divided by the desired wire size's ampacity rounded up if there is a remainder. An example: If I have a 361 Full load Amp motor from the NEC table and I calculated the motor circuit...

Homework Statement A cylinder rotating uniformly about the x' axis of S' will seem twisted when observed instantaneously in S, where it not only rotates but also travels forward. If the angular speed of the cylinder in S' is ω, prove that in S the twist per unit length is yωv/c(squared)...

My professor asked the cost of running a hair dryer of 1500 W for 15.0 minutes for 5 days a week for 4 weeks. The utility company charged $0.60 per kWh. Instinctively, i thought to combine 1500 W with the 15.0 minutes into my version of "kilowatt per hour". 1500 W * \frac{1 KW}{1000 W} =...

Hey, A coulomb is the amount of charge that passes a point through a wire carrying one ampere for one second. Voltage is a measure of electrical potential energy in units of volts or joules per coulomb (energy/charge). Then 1 volt means 1 joule per coulomb; 2 volts mean 2 joules per coulomb...

Homework Statement long solenoid of n turns per unit length is wound upon a cylindrical core of radius a and relative permeability. The current I through the solenoid is increasing with time t at a constant rate. Obtain expression for the rate of increase of stored energy per unit length...

What is the concept of per second per second?? Like acceleration?? I'm in my final year of college and I'm struggling to get a clear idea on the concept of per second squared. I mean a meter per second yeah that's understandable, it's just mean your moving a meter per second, so 5 seconds...

Homework Statement An astronaut rotates at the end of a test machine whose arm has a length of 10m. If the acceleration she experiences must not exceed 5g (g = 10 ms^-2), what is the maximum number of revolutions per minute of the arm?Homework Equations T = (2πR)/v V = (2πR)/T Ac = V2/rThe...

Hi. I work with rain (precipitation) time series, and would like to extract time statistics: - precipitations per month - precipitations per year - precipitations per month and year - precipitations per hour - precipitations per month and hour - mean precipitation, deviation, ... I...

How about Apple starting a $2 per hour minimum wage for its vendor employees? It would be great PR.

Hello all I was wondering if anyone could help me with the following:- The equation of a line is Y = -0.00331x + 9907.333. The equation represents distance (x) and elevation (y) The gradient is -0.003311. What is number represents is for every 1 unit I move in the x plane I move...

Homework Statement i) The average concentration of 222Rn in air inside a building is 20Bqm-3; what is the average concentration of Rn in atoms per cubic meter? ii) In a sealed room of volume 50m3 what activity of 238U in a piece of porous rock would eventually give rise to this 222Rn...

Why is the number of charge carriers per unit volume is inversely proportional to resistance?If there is more charges carrier, it doesn't increase the collision between free electron which causes in increase of resistance?sorry for my unclear concept of Electricity circuit.I hope there will be...

Homework Statement Consider a small portion (area=A) of the inside wall of a container full of gas. Show that the number of molecules colliding with this surface in a time interval Δt is PAΔt/(2mvx avg), where P is the pressure, m is the average molecular mass, and vx avg is the average x...

Homework Statement A metronome is a device used by musicians to help them adjust the timing of their music to a standard number of beats per minute. The position of the moveable slider determines the frequency. It is possible to build a simple mechanical metronome using a light stick...

Hello, Related to a thought of why animals don't use photosynthesis (typical answer is that photosynthesis would provide only marginal energy compared to the needs of an animal), I am interested in how much energy does a plant produce using photosynthesis? Any example or estimates is good...