# Power Definition and 307 Discussions

A power outage (also called a power cut, a power out, a power blackout, a power failure, a power loss, or a blackout) is the loss of the electrical power network supply to an end user.There are many causes of power failures in an electricity network. Examples of these causes include faults at power stations, damage to electric transmission lines, substations or other parts of the distribution system, a short circuit, cascading failure, fuse or circuit breaker operation.
Power failures are particularly critical at sites where the environment and public safety are at risk. Institutions such as hospitals, sewage treatment plants, and mines will usually have backup power sources such as standby generators, which will automatically start up when electrical power is lost. Other critical systems, such as telecommunication, are also required to have emergency power. The battery room of a telephone exchange usually has arrays of lead–acid batteries for backup and also a socket for connecting a generator during extended periods of outage.

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2. ### Power required to climb a 20-m-tall building in 55s

Summary:: A 90 kg firefighter needs to climb the stairs of a 20-m-tall building while carrying 40kg of gear. How much power does he need to reach the top of the building in 55s. So first the total mass of our system is 130 kg. Using this mass, I found the potential energy the firefighter would...
3. ### I Negative thermal Power

I have a cylinder that is separated with an insulator. In the internal cylinder there is a thermal source, while outside the insulator we have a thermal sink. The power of the internal cylinder is positive, while of the external one in total is negative. How I should interpet the results. Like...
4. ### I Long compound bow limbs

Hello If a compound bow has longer limbs will it have more power? Longer limbs means more limbs, hence more tension is building when limbs bend. That tension transfers to the bow string. Is this a true statement. I know there are other factors for making a powerful compound bow. Is long limbs...
5. ### Intensity of a laser beam at a certain distance

I haven't been able to pinpoint a definition of "angular divergence" of a laser so by pure intuition I assumed it would be something like ##\theta=\frac{2R}{D}## and with that I have that the radius of the lase beam is ##R=\frac{D\theta}{2}=90\cdot 5 \cdot 10^{-6} m=450\ \mu m## so...
6. ### Find the pressure drop and power loss of pipe when elevation changes

Summary:: I can’t get the correct answers, I think I haven’t fully understand the theory behind them The answers are given in the picture
7. ### Engineering Induction motor calculation problems

Given the following input parameters: Parameter Value Rs (Resistance through stator) 1.4 Ω Rr (Resistance through stator) 0.7 Ω Ls (stator inductance) = Lr (rotor inductance) 0.002 H xs = xr = 2*π*f*Ls 0.6283i Ω Lm(magnetic inductance) 0.01 H xm = 2*π*f*Lm 3.1415iΩ f (frequency)...
8. ### Engineering Induction motor calculations

Given the AC Induction (asynchronous motor) in 3 phases: Parameter Value Pn (Nominal Power) = Pmechanical (output power at the shaft) 5 kW = 5000W uls (Voltage through the stator line) 220 V fstator (stator frequency) 50 Hz p (Number of pole pairs) 2 LFe (Iron loss) = Lmechanical...
9. ### Work done on moving a submerged object

I first worked out the buoyant force using rho = 1000, g = 9.8 and V = 1. (this gives Fb = 9800) I then worked out Fg of the tank (5 x 9.8 = 49) Then I used Fnet = Fb - Fg - T = 0 to work out tension as 9751. I thought the work done would be the work done by tension (9751 x 50.4), but I'm not...

11. ### Need help with Axial flux generator

I am sure axial are used in wind turbines so i will use it as my example. Say you are using the wind turbine to generate power but its getting to windy and you want to slow down the turbine to bring it to a stop. What i want to know is ... If you can cut off the power that's been generated...
12. ### How do atheletes sustain high power output, physiologically?

I am ~180lbs and have been lifting weights for about 12 years straight. I have also been running 3-4 times per week for the last 8 ish years. I have recently gotten into cycling, and noticed at the gym on the Schwinn "spin" bike, I will have peaks of around 400-500 watts, but it's definitely...
13. ### How to calculate the electrical power output using the Organic Rankine Cycle?

Basically this would be a closed loop geothermal system for electrical power generation. The system would consist of 2 Horizontal Wells connected creating a U-shaped closed loop cycle using thermosiphon effect, with constant recirculation. It's not really a conventional geothermal power...
14. ### B Power of ten and math power notation

Dear PF Forum, I watched this video 10 ^ 10 ^ 10 ^ 5600 The narative says, It is 1 followed by 5600 zeros But that's not what I think, I think it is 1 followed by I don't know. What does this number means? Is it A: 10 ^ (10 ^ (10 ^ 56))) or B: ((10 ^ 10) ^ 10) ^ 56? It says that "As...
15. ### Engineering Small signal AC modeling for a boost converter with resistive losses

I've attached my attempts at the solution and the actual question below. I believe the only issue I am having is I don't know how to get rid of "I" in both my final inductor and capacitor equations as the HW states I shouldn't have anything in term of I. I believe I need to put "I" in terms of...
16. ### Power Line Losses

This problem is trivial, but I cannot make sense of my answer (I am not even going to bother with the cost calculation. First, I used P=IV with P=15 MW and V=120 V to find I=125 kA So far so good. Then I calculated the resistance per meter as R=\rho\ell/A=(1.68\times 10^8\Omega\cdot...
17. ### Conservation of Energy Problem (Power)

Hello there, I was trying to solve this problem. I have no problem with part A and C. But in part B, my guidebook arrived with different answer. Can anybody point out what my mistake is? I am using the same method as the elevator motor problem which states : "A 650-kg elevator starts from rest...
18. ### Power of a particle on a wave

I've marked the right answers. They mainly indicate at power carried by the particles being zero, and here is my doubt- why should it be zero? Shouldn't it have some definite value? I do understand that the kinetic energy is max at the y=0 and potential energy is max at y=A, but I don't know...
19. ### Power generated by an engine

I'm really struggling with this problem. I can't understand which are the forces that i need to calculate work. Probabily when the sand falls the force of which i need to calculate work is weight force, but which is the force that carries the sand at the top of the roller?
20. ### Power required to reach X velocity in X time with drag

Hello, I wrote a program that adds force to a car like so: Engine Force = Power / Velocity Drag Force = -Velocity² Net Force = Engine Force - Drag Force = Power / Velocity - Velocity² I'd like to determine power based on how fast I want a car of a given mass to reach a given speed, for...
21. ### Determining the power of frictional force

I can say that the frictional force always against the rolling sphere and the velocity is increasing for the ball. So The dot product F.v keeps on getting more and more negative, so how can the Pf remain constant? Well the velocity increases along the incline and the force of gravity is down...
22. ### Calculate the output power for da Vinci's tank mechanism

Hello everyone. I'm working on 3D animation about da Vinci tank and why it doesn't work. Please help me find out how to compute: 1: how many men need to move this machine 2: what power on wheel can produce different number of man, like 1, 2, 4, 8.. vehicle mass = 8t men strength = 60kg lever...
23. ### Why Isn't Horsepower an SI Unit, Despite Its Popularity?

When we talk about engines on automotive industry (cars, motorbikes, trucks, etc.), we often refer the power produced by such engines by horsepower. But when we talk about electricity, the power is measured in kilowatts. Despite the former case is highly popular, why isn't horsepower considered...
24. ### Calculate the current in all parts of this electric circuit

In the circuit below, the output is 23 W across the resistor with the resistance 6 Ohm. Calculate the amount of current in all parts of the circuit as well as the polarity and EMF ε of the unknown battery. Circuit: My attempt: I get 6 unknowns with 5 equations. I don't know how to find the...
25. ### Must a load consume the entire available current or only what it needs

So if I have a source of 5V and 20 amp then the maximum power I can get from the source will be: $$P_{max} = 5*20 = 100W$$ but my load can only take in 5 watts, it will blow up. But, does this have to happen or does my load only take what current it needs? My guess is that the load takes in...
26. ### Power in Cycling Question

OK, so I tried to relate the equation P=Fv to the given equation that Pave^2= 3(Pftp^2)/Nh. I put Nh in terms of distance to satisfy the requirement that the answer should be in terms of Pftp and distance by saying Nh = distance/Vave. I also substituted Pave with Fvage. (FVage)^2 =...
27. ### How to determine the power of a rotary lobe pump?

Want to know how to get the actual power the pump needs. I can measure the flow rate by the flow meter and count the revolutions of the pump. But selecting the proper motor for the pump would be a problem. So I want to know how to determine the power of the rotary lobe pump and generate the...
28. ### Engineering Finding voltages in a linear circuit

From the circuit I have: ##-v_b + v_a + V = 0## ##v_b - V = v_a## ##i_1 = (v_b - V)/R_1## ##I + i_2 = i_1## ##(v_b - V)/R_1 = I + v_b/R_2## From this last equation I get ##v_b = 10.8## and hence ##v_a = 5.8##. However, apparently that is wrong. (And hence my answers to #2 were all wrong as...
29. ### Introductory Circuit Analysis—power ratings

I am going through "Circuit Analysis for Dummies". On pg 18, it says, "If you calculate the power dissipated as 0.1 watts, then a 0.25-watt resistor can handle this amount of power. A 0.125-watt resistor should be able to handle that amount as well, but when it comes to power ratings, err on the...
30. ### Induction stovetop design: am I using these equations correctly?

I've been told an effective induction stovetop needs to deliver about 1000W of power. I have magnet wire that can tolerate at most about 0.2A of current, and was planning on using a 60Hz wall outlet as my source (obviously I'll need to bring down the outlet current quite a bit). So the energy...
31. ### Maximum power in this resistor circuit

My attempt-: So the resistance is coming to be negative.Can anyone tell me my mistake.Thanks.
32. ### I Calculate Retinal irradiance - from photometric units

I have been trying to calculate what retinal irradiance value I get with a 1 blue LED system. Since the manufacturer didn´t give the spectral distribution information, I will approximate LED as a monochromatic one (using the 460 nm peak). From the datasheet, the LED intensity range goes from 6...
33. ### Power spent to keep a spring compressed

I was wondering, I have an engine that should keep a spring compressed. How can I calculate the power necessary for this? The work is Force x Distance, as there is no distance, there is no work, so no power... But obviously to keep the spring compressed the engine will have to produce a...
34. ### How is it possible to use only 1000 W to transfer 10,000 BTU/h?

Hi, I was reading a newspaper article on the energy efficiency of commonly used air conditioners in homes. Then a doubt arose when the article informed me that there are air conditioners that have an energy efficiency of 10 BTU/watt. That means a classic 10,000 BTU/h air conditioning machine...
35. ### How to calculate mechanic power a person outputs?

Hey all, I am doing some work to brush up my acoustics and one of the problems I came across this goes like this (translated, so sorry for potential grammar mistakes although I'll do my best to avoid them): A singer exhales 0.1 Litre Air per second. The 'overpressure' (pressure difference, so...
36. ### What is AP layer in Ansys RedHawk? [SOLVED]

What is AP layer in ansys redhawk ? I have list of layers I see in ansys redhawk tool, there are different metal and via layers , instances etc and there is a layer called AP in the end, What is this layer or where can I find more information bout it?
37. ### What is the power input of a motor pulling up an elevator?

Homework Statement Once under way at a steady speed, the 1100-kg elevator A rises at the rate of 1 story (2.74 m) per second. Determine the power input Pin into the motor unit M if the combined mechanical and electrical efficiency of the system is e = 0.76. Here is a link to the diagram for...
38. ### Torque required to tilt 1200 kg mass?

Object to be tilted = 1200mm diameter cylinder Cylinder height = 2.5 meter weight of tilting assembly = 1200 kg Cylinder is on platform which is "L" shaped and tilting point is on that corner of "L" as in attached image. Shaft diameter on which it is tilted id 63mm Angular acceleration = 0.05236...
39. ### China's Experimental Advanced Superconducting Tokamak (EAST)

A team of scientists from China's Institute of Plasma Physics announced this week that plasma in its Experimental Advanced Superconducting Tokamak (EAST) would be ready to begin attempting to generate more energy than it uses, in a world first. I am dubious about more news that comes out of...
40. ### Deriving Voltage from the Inductor Equation

Homework Statement L = 20mH = 20 x 10-3 H i = 40 mA for t≤0 i = A1e-10,000t + A2e-40,000t A for t≥0 The voltage at t=0 is 28 V. I have to find the equation for the voltage for t>0. Then I have to find the time when power is zero. Homework Equations v(t) = L* di/dt p(t) = L*i* di/dt The...
41. ### Emptying a well using a pump

Homework Statement A well has a diameter of 6 m and a height of 15 m.2/3 of volume of the well is filled with water.A pump can vacate 1/3 of volume of water from the well in 7 minutes 20 seconds.What is the power of the pump? Homework Equations W=mgh, P=W/t The Attempt at a Solution The...
42. ### How can I calculate the number of photons with this data?

The problem says: A radio station emits electromagnetic wave with a frequency of 100MHz (102*106 Hz). a)What's the energy of this radiation's/glow's photon? (Solved, i found 6,63*10-26 J) b)Compare your calculation with the energy of another visible radiation/glow, with a wavelength of 600nm...
43. ### Determining the flow rate for a cooling system

MODERATOR'S NOTE: HOMEWORK INCORRECTLY POSTED TO CLASSICAL FORUM, SO NO TEMPLATE I need help with the following question: Please have a look at the question and my attempt at the solution. Alternative cooling systems are considered for a large computing centre requiring 1 MW of cooling...
44. ### Worksheet Problem about Power (average power of a car accelerating up a hill)

Homework Statement A 1130 kg car is initially at rest when it accelerates up a 21 m high hill. When it reaches the top of the hill it is traveling at 18 m/s. If it takes 6.5 s to reach the top of the hill, what was the average power of the car? Homework Equations W = Fd P = w/t The Attempt at...
45. ### I Iterating powers of complex integers along axes of symmetry

I am exploring the behaviors of complex integers (Gaussian and Eisenstein integers). My understanding is that when a complex integer z with norm >1 is multiplied by itself repeatedly, it creates a series of perfect powers. For instance, the Gaussian integer 1+i generates the series 2i, -2+2i...
46. ### Potential Energy of a Particle | Work done by Conservative Forces

What is a conservative force and how do you determine the work done by it. It is an interesting relation between the work done by such a force and the potential energy and kinetic energy of a particle.
47. ### I Mutually disjoint sets of all integer powers?

I identified what appears to be a partitioning of all integers > 1 into mutually disjoint sets. Each set consists of an infinite series of integers that are all the powers of what I am calling a "root" r (r is an integer that has no integer roots of its own, meaning: there is no number x^n that...
48. ### How to use Thevenin to find R and I?

Homework Statement In the circuit shown, in the image, the variable resistor R is consuming maximum power. Determine: a) resistance for R b) power for R c) current for R3 and its direction Homework Equations The Attempt at a Solution I tried getting IA(the direction is shown with arrows...
49. ### How to find power and voltage using the mesh current method?

Hi. I am practising for my test and since I don't have the correct answers, I don't know if what I'm doing is right. I tried to solve this problem, can you check it and correct if it's wrong? Here's a clearer picture of the circuit. I suspect Uab isn't right, but am not sure. Thanks...
50. ### Determining Work Done by a Person on a Luggage

I'm trying to determine the work done by a person as they pull a luggage up a ramp. The ramp has a height of 5 m and the distance the person walks up is 20 m. The weight of the bag is also 10 kg. I am trying to compare the work done by pulling the luggage up a ramp to carrying an equally heavy...