# Questions tagged [power]

The time rate of change of energy

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### Inverse Square Law Two Formulas [closed]

I read two formulas: $$\frac{p}{4 \pi r^2}$$ and $$p \frac{1}{d^2}$$ I don't understand. I do have my own guesses but I want to know so I'm not wrong.
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### If the rotational speed of a turbine at a power plant doubles, does its voltage, current or power double? [closed]

Somehow, I cannot find a simple answer to this question, or a simple equation or equations... All other things being equal, if a turbine at your local power plant instantaneously doubles its rpm (or, ...
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### Would it be possible to create a spherical csp that uses a solar array to direct light into a sphere where it can reflect back into itself?

I’m just a student who can’t find any answer about this. Perhaps because I didn’t look hard enough, regardless I’m curious. Concentrated solar power is a really big step towards solar energy. Using an ...
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### Would it be possible to extract/filter out two waves of different power but same frequency?

If we can use say Fourier Transform to extract every individual frequency on a signal, can we do the same for power? I was figuring if it would be possible to extract them for further inspection on ...
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### Relationship between work and potential energy

Ultimately what I am trying to do here is convince myself that the following relationship holds: $$F = -\frac{dU}{dx}$$ for a force $F$ and a potential function $U$. We have that the work $W$ can be ...
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### Calculate power for a non-constant force [closed]

Suppose there is a body of mass $m$ in a horizontal plane, with initial velocity $v_0$, that is subjected to a force $F(t)$ (the force depends on time). How can I calculate the power developed by the ...
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### What is the angular velocity of a wheel as a function of time as it is spun up by a DC motor?

For the sake of concreteness, let us consider a brushed DC motor. I am trying to predict how much a wheel spins up when it is connected to a DC motor for a certain amount of time $t$. Let's say I ...
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1 vote
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### What is the work done in lifting the bucket? [closed]

A bucket is tied to a well with a chain 20 meters long to lift water. If the weight of the chain is 2 kg per meter and the weight of the bucket filled with water is 20 kg, what is the work done in ...
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### Does the resolution of a timeseries affect the estimate of the power-spectrum?

I have been trying to estimate the power spectrum of a timeseries using fourier transform. I noticed that by downsampling my timeseries I get a different spectrum as shown below Here you can see ...
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### Actual power consumption of an irregular measure (GPU/CPU) [closed]

Hello and my apologies if this is off-topic or really too basic. My math and physic days are really far far away.... I want to measure the energy consumption of both the GPU and CPU of a computer ...
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### tGiven a propulsion system with constant power, how long does it take to travel a given distance in space? (non-rel. and relativistic)

Suppose a space ship of mass $m$ is travelling away from our solar system, starting with "starting speed" $v_{start} > v_{escape\ \odot}$, meaning it will escape sun and have some ...
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### What is the dependence of fusion power of the particle energy at fixed pressure?

The fusion reaction power depends on the reaction rate. The reaction rate depends on the concentration and the cross section.The cross section depends on the energy of the particles or temperature. ...
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1 vote
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### Transformers in Power transmission [duplicate]

Recently I learnt that transformers are used in the national grid to increase the voltage, so we get less current. But my understanding V=IR and by increasing the voltage we get more current, so what ...
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### How to calculate the energy and power of the force of lift that acts on a cruising plane?

Say we have a plane flying at constant speed and altitude. Looking at the y axis, the lift cancels out the force of gravity as it maintains constant height. I want to calculate the energy used to ...
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### Reflection of power at low frequencies?

Assume you have an AC signal source outputting 0dBm of power and connected to that are two resistors one of 50 ohms and another 100 ohms. The reflection coefficient is given by: It seems like this ...
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### 'Distanceless' force for aircraft seems to break laws of physics

When an jet is flying, its engines produce thrust. I assume that the thrust and fuel consumption is about the same at all aircraft speeds. However, when the airplane is going faster, it produces more ...
1 vote
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### Calculate uphill efficiency on different gears [closed]

I was interested to find whether it would be more efficient to climb a hill on a lower gear, so I did some calculations. I have the following data of a custom vehicle: Gear Drive force (N) Max speed (...
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