The time rate of change of energy

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0answers
25 views

Forces in material removal (cutting, grinding, sanding, etc.)

A. Suppose a circular saw is spinning at a certain angular speed. When it starts to cut into the material, removing chips of the material or abrading it, the speed drops. The drop in speed depends on ...
1
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0answers
26 views

which motor to choose? [closed]

This is a really stupid question, but im not quite able to figure out which motor to choose. I need to move about 1kg of weight at about 1.2 meters/sec on a conveyor belt using a stepper motor. What ...
0
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1answer
81 views

Intensity of a standing sound wave at displacement nodes?

We know $$P = F\cdot v$$ where $v$ is the velocity vector. Since at the "displacement nodes" in a standing sound wave the velocity of the particles is always 0, the Power must be 0 and hence the ...
0
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1answer
43 views

Calculate spectral radiance at defined wavelength given radiant power

I am struggling with what I think is actually a simple problem. I have an LED that emits infrared light (950 nm). It is part of a sensor system. The manufacturer claims it has a radiant power of 3000 ...
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2answers
84 views

Couldn't high gear ratio replace need for high torque engines?

I've noticed that there is a correlation between displacement and torque, so trucks, SUVs etc. have large displacement engines to produce lots of torque to move heavy loads. Sports cars have lower ...
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4answers
78 views

Why do coal power stations not directly use combustion to turn the turbines?

Why do coal power stations run by creating steam rather than from the expansion due to combustion? I understand that in order to generate electricity in a coal power plant, steam is usually produced ...
-1
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1answer
51 views

Power Dissipated by Resistor in AC Circuit [closed]

I'm having a problem with the following review question: Given the circuit: I am asked to find the power dissipated by R1 and C. I know that for C it is 0. For R1, I know I need to use Vrms ...
1
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1answer
85 views

I m just try to make Free energy using buoyancy [duplicate]

Can I make power (electricity ) using buoyancy see diagram. if this diagram is possible then how much power i get . I just need formula for upwards speed.
1
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0answers
43 views

Luminous intensity: from Volt to Candela/m2

I use a probe for converting optical power to an electrical current. I need to convert Volt to candela/m2. The sensor, a photodiode, measure the brightness of the monitor leaning the probe on the ...
1
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3answers
111 views

Power statement is valid for MW Or KiloWatts? [closed]

If I can talk to someone and tell him that a new power plant inaugurated by Prime Minister will produce $60$ megawatts per hour, will it be true to use $\mathrm{MW}$ unit for Power?
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2answers
63 views

Using gravity's force to do work?

Since gravity is everywhere and we don't need to do anything to feel it and interact with gravity, can we somehow extract the gravity force to do work and power machines? For example, we've nuclear ...
0
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3answers
220 views

Why does the work-energy theorem need to include internal forces?

Can anyone kindly explain me why work energy theorem must also include internal forces? The proof of work energy theorem is derived from Newton's laws of motion, but Newton's laws of motion don't ...
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3answers
1k views

If UV radiation 1 cm away from the halogen bulb is equal to Sun's radiation, what is the level of radiation 1 meter away?

Halogen light bulbs emit some amount of UV radiation, and some sources consider them dangerous. Here it is written, that UV radiation (of certain types) from a particular halogen bulb was equal to the ...
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2answers
109 views

What's the right way to calculate power consumption over a month given a rate per minute?

When I was searching for power required to lift an object, i found that, for example: $100\ \mathrm{kg}$ to be lifted 3 metres in 5 seconds. (vertical) Answer: $$\begin{align} ...
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votes
1answer
26 views

Finding the distance travelled during change in velocity from $v_i$ to $v_f$ [closed]

A constant power is applied to a particle of mass m. The velocity of the particle increases from $v_i$ to $v_f$. We have to find the distance travelled by the particle during this interval.(neglect ...
0
votes
2answers
50 views

How are superconducting magnets powered?

Since the resistance of a superconducting circuit is exactly 0, it would try to draw infinite current from a power source, since P=I^2*R. For a finite power source, I-> infinity as R->0. Correct? ...
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votes
1answer
81 views

Finding the resistance of platinum wire [closed]

Im currently lost on solving this potentially simple electricty question and was wondering if anyone in this community could hint me or tell me which equations and why these equations would be ...
1
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2answers
80 views

Which expression to use for electrical power?

We know that electric power can be written as $P=VI$, or $P=\frac{V^2}{R}$, or $P=I^2R$. But when to use which one? Sometimes two different formulas give different results! Please explain with ...
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2answers
42 views

Shorting a Superconducting Coil with A/C

When a superconducting coil carrying a direct current is shorted, it continues to carry the current without loss (approximately), assuming it stays cooled and superconducting. What would happen if ...
-1
votes
1answer
117 views

Find the velocity of water if power and mass is given [closed]

A pump of 200W power is lifting 2kg water from an average depth of 10m per second. Find the velocity of water delivered by the pump? $$P=200W$$ since the water is lifted per second ...
68
votes
7answers
9k views

Why does public mains power use 50-60 Hz and 100-240 V?

Is there a physical reason behind the frequency and voltage in the mains electricity? I do not want to know why exactly a certain value was chosen; I am rather interested to know why that range/order ...
0
votes
1answer
147 views

Nuclear to Electricity Energy Conversion

Currently nuclear power generates heat, which heats water into steam that turns conventional turbines. The energy conversion is as follows: photonic->heat->kinetic->electric This would result in low ...
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votes
1answer
50 views

What holds good? [closed]

If the 1 ohm resistor is replaced by a 0.2 ohm resistor. what will be the current flowing through ? What actually determines it ? the OHM'S LAW or POWER CONSERVATION ?
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1answer
61 views

How much power is needed to drive two times faster?

Suppose a cyclist riding at speed $v$ decides to accelerate to speed $2v$. Does she have to generate $8$ times more power to sustain that speed? $P_1=F_dv$ If we double the speed, (it usually ...
8
votes
3answers
2k views

Trying to understand jet engine [closed]

I'm trying to understand at a high level how a jet engine works. I want to know if the following summary I wrote is more or less accurate: The jet compresses regular air into a combustion chamber. ...
-1
votes
2answers
135 views

More torque or more horsepower? Which engine is more powerful [closed]

Two internal combustion engines : $250\,\mathrm{hp}$ and $900\,\mathrm{Nm}$ torque $770\,\mathrm{hp}$ and $790\,\mathrm{Nm}$ torque Which of the above two engines will be more powerful? P.S. ...
2
votes
1answer
32 views

Radioisotope beta decay generator

Why are there no electrical generators utilising the electron/s of beta decay from a radioisotope for generating a working current? For example, how much radioisotope would I need to generate 1A or ...
-1
votes
1answer
111 views

How to find power dissipation of bulbs [closed]

The following circuit is connected in series and $240V$ power supply. Bulb $A$ has $240V$, $100W$ rating. Bulb $B$ has $240V$, $500W$ rating. Calculate the power dissipated at bulb $A$ and $B$ ...
0
votes
1answer
137 views

Power output of electrical hotplate

This sounds simple but i need some clarifications. I am using a hot plate to heat a solution in an oil bath. The power rating and maximum temperature of the hot plate is 1520 W and 500 oC ...
-1
votes
1answer
578 views

Average Power and Instantaneous Power

I am confused between the usage of the terms average power and instantaneous power. What is the main difference between the two?
2
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2answers
115 views

Could a civilisation contact us by laser from 50 light years away?

The Kepler Space Mission has discovered over 1,000 planets. These discoveries may increase the confidence of some people that other civilisations exist. That is an opinion issue, and not what I want ...
1
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1answer
95 views

Why are GPS transmitting signals made so weak?

Twice this year, my car's GPS receiver got totally lost. It seemed the cause of this was heavy cloud, (because I can't think of any other reason), and the GPS stayed in "Recalculating" mode, until ...
0
votes
2answers
105 views

Does a switched on power socket consume electricity? [closed]

Lets say I have a TV and a power socket but the TV switch is off however the socket switch is switched on, so will it consume electricity?
0
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1answer
57 views

Formula connecting Force and Power

Is there such formula? There probably is of course, but i would like a very concise description of how to derive it, in order to better understand myself. Thank you in advance.
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0answers
85 views

Calculating the force applied by an electromagnet on a ferromagnetic object [closed]

I know how to calculate the force applied on a magnetic object by an electromagnet at $n$ metres distance using $$F = \frac{(N \cdot I)^2 \cdot k \cdot A} {2 \cdot g^2},$$ but how would one calculate ...
0
votes
0answers
185 views

Work done by flow of a fluid

I'm looking at the power a flow of steam in a turbine. I originally assumed that the kinetic energy of a moving section of steam was equal to (let $V$ be volume, $\rho$ be density, and $v$ be velocity ...
0
votes
1answer
260 views

relationship between voltage and current

I know that this question had been asked many times but I think it will be a new info in Ohm’s law: $$R = V/I$$ So Voltage is directly proportional to Current In Electric Power’s law: $$P = ...
0
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1answer
136 views

Power of a wave in a string

My text of physics, Gettys', shows how the energy, both kinetic and potential, of a small element $\Delta x$ of a string, through which a wave (whose wave function is $y:\mathbb{R}^2\to\mathbb{R}$, ...
2
votes
5answers
183 views

No need Power to fly ? Paradox [duplicate]

I would like to know how much power I need for magnetic levitation. $$P = Fv.$$ $F = F_g \approx \text{mass} \times 10$, okay. But $v = 0$! I can't believe I need no power to keep an object in the ...
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2answers
325 views

Which power equation to use: $P = I^2 * R$ or $P = V^2 / R$?

Given are ideal max voltage $V = 200\;\mathrm{V}$ and max current $I = 5\;\mathrm{A}$. Therefore: ideal resistance is $$R = \frac VI = \frac{200 \;\mathrm{V}}{5\;\mathrm{A}} = 40 ...
1
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1answer
180 views

How is power of a water pump related to amount of water delivered from pipe?

My book says: Suppose a pump motor is used to deliver water at a certain rate from a given pipe. To get n times the water from same pipe in same time the power must be increased by $n^3$ ...
0
votes
1answer
27 views

Why does power loss in pure metal caused by temperature is calculated base on $P=I^2R$ but not $\frac{U^2}{R}$

$$P=I^2R=\frac{U^2}{R}$$ The metal's resistivity is temperature dependent, neglect the change in size by temperature. The power loss of a pure metal when it drop form temperature $T_1$ to $T_2$ is ...
0
votes
4answers
738 views

How power lines use high voltages with a low current?

I've read that power lines use high voltages and low currents to reduce power loss due to resistance. Looking at the formula for power - P = VI So to increase P, you increase V rather than I for ...
0
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4answers
166 views

Engine fuel consumption vs power

Something that has bother me for a long time is why a 600 hp engine uses more fuel per kilometer than a 80 hp engine. Let pretend I have two equal cars (same shape same weight etc) except for the ...
17
votes
2answers
4k views

How big is a 1kW fire?

What is the size/scale of a wood fire that is producing 1kW? I'd like to improve my ability to conceptualize various power scales.
0
votes
1answer
51 views

How to Calculating power using smart phone?

I'm writing a smart phone app and one of it's functions is to calculate power of the vehicle that the phone is travelling in. The user enters the total weight of the vehicle and the app uses the ...
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3answers
2k views

Calculate acceleration from power [closed]

I am currently programming a simple computer space ship simulation. This is just for fun to train my programming, 3D graphics and a little bit of physics skills. What I want is the user to pick a ...
1
vote
2answers
72 views

How to improve the power output of an AC motor without changing its characteristics [closed]

I have an AC motor at 230V/50Hz and 2.2 KW power that will power a drilling bit for cutting wood. The motor has 3000 RPM, but if I attach the drilling bit (8 cm wide, 15 cm long and with a step of 8 ...
0
votes
1answer
374 views

Can I convert Power to Force?

I just realized that I have some issues with physics: I cannot just convert Power to Force (different units), $P = F * v$. But am I not able to calculate the force on a car that accelerates with a ...
25
votes
5answers
3k views

Is it possible to build a thermoelectric nuclear power plant?

Current nuclear power plants are essentially an enhanced version of a kettle, which seems like a stupidity caused by a lack of other options. We heat the water which turns to steam which rotates the ...