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# Questions tagged [power]

The time rate of change of energy

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1 answer
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### How fast do you need to travel downwind to obtain the maximum amount of power from the wind?

Suppose you are traveling downwind, in a wind speed of $x$ meters per second. If you are stationary, the wind speed relative to you will be the highest, but you will not be moving, so no work/power is ...
• 1,019
1 vote
2 answers
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### Are $U^2/R$ and $I^2*R$ the same? [duplicate]

We know from Ohm's law that $U^2/R$ and $I^2*R$ are equal. Generally, high-voltage transmission is used to save electricity. When calculating the amount of heat generated in this case in terms of $I$, ...
3 votes
3 answers
472 views

### Electric power transfer

I'm reading electric power from the book "Fundamentals of physics textbook by Robert Resnick" and I have a question about the interpretation of the text. First it says "The principle of ...
0 votes
2 answers
43 views

### Is energy and work the same in numerical basis? [duplicate]

Consider this formula: P=W/t where p is power, W is work, and t stands for time. and also this formula: E=Pt , where E is energy, P is power, and t is time. so by the substitution property, you can ...
1 vote
0 answers
22 views

### Power Number of Impellers in non-Newtonian fluids

I have been working on a project involving mixing a non-Newtonian fluid. To begin with, the fluid exhibits a shear-thinning behaviour that follows the power law: $$\tau = K \dot{\gamma}^n$$ As for the ...
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1 vote
1 answer
52 views

### Doubling up on Ear Protection NRR Equation

I'm planning to go to shooting ranges soon, and am looking for ear protection. Let's say that I get an earmuff with a noise rating reduction (NRR) of $X\ \textrm{dB}$ and earplugs with $Y\ \textrm{dB}$...
• 111
0 votes
1 answer
108 views

### Understand power rating in layman terms

I have recently started the chapter of electricity of class 8. I am not understanding the concept of power rating of appliances. When we say that a bulb is rated 220V-100W, which means, according to ...
0 votes
0 answers
36 views

### What is the solar radiative power on a clear sky day through a surface which is parallel to the sun's incidence on Earth?

Assuming that the solar power through the incident surface is known. How can we calculate or estimate the radiation through the parallel surface assuming a clear sky? Looking for watts per square ...
• 111
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6 answers
141 views

### What is electromotive force? What's its relationship to Voltage? + clarification of confusion

So first of all, yeah I know that the electromotive force is not a force (the name was coined by Alessandro Volta I think). About Power and dissipated power The power with wich a battery provides the ...
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1 vote
0 answers
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### Output of ventilator and air friction

Imagine you have a ventilator with straight rectangular ventilator blades which are rotated at some small angle from a perpendicular line to the rotating axis. The ventilator has 100% efficiency (all ...
• 11
1 vote
1 answer
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### Radiation power emmited by a material with two different temperatures [closed]

Let's consider a cylindrical sample of a solid material surrounded by air. From $0 \leq r \leq r_1$ the temperature of the material is $T_1$ and from $r_1 < r \leq R$, $T=T_0$ which is also the ...
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1 answer
141 views

### How do I calculate change in flux in an augmented rail accelerator without violating conservation of energy?

Suppose I have two rails and a wire connecting them I'd like to accelerate. Then $\frac{d\phi}{dt}=Bvl$, where $B$ is the magnetic field strength where the wire is, $v$ is the velocity, and $l$ is the ...
4 votes
3 answers
158 views

1 vote
1 answer
52 views