# Questions tagged [power]

The time rate of change of energy

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### Discrepancy between two calculations for the power provided by a pump

I am a high school student and I am very confused in a question related to power. I was able to get the right answer but i am not satisfied with the results I get. The question is A motor pumps ...
58 views

### asking a question on POWER [closed]

I am a high school student and I am very confused in a question related to power I was able to get the right answer but i am not satisfied with the results I get . The question is "A motor pumps ...
39 views

### When to use Ohm's law as opposed to using power formula?

I am a mechanic trying to gain a better understanding of electrical theory on vehicles. I have a sound understanding of Ohm's law and also the power formula (Power = Voltage x Current) However, I am ...
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### What is the power while accelerating a bicycle?

With respect to this question, the power on a accelerated body, that moves in the same direction of the acceleration, can be calculated by $W = Fv$, where $F$ is the external force and $v$ the ...
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### Work Equals Torque? Horsepower, Pulleys

While reading one definition of torque, I saw its units are Newton-meter, which is the same as work. But sources usually make it a point to emphasize "even though both work and torque units are ...
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### Instantaneous power for a variable force

I know that instantaneous power is defined as the time derivative of work done. For a constant, it is easy to prove that this is just the dot product of force and velocity. However, is Instantaneous ...
35 views

### Calculating the time to perform work on rolling shutters

I have rolling shutters, e.g.: I am trying to determine how much time it takes to raise/lower the shutters a specific amount. (Because of the physics involved, the time is non-linear relative to the ...
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### Why does ground reaction force decrease at the start of a vertical jump?

I don't understand why reaction force would decrease at the start of a countermovement jump. I've tried looking at this diagram and considering moments and how lowering the position of the center of ...
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### Power consumption of vacuum tube [closed]

What is the power consumption of a vacuum diode? (or vacuum tube). I'm interested only in the "Anode supply voltage", this source typically has values of around $100\ \text{V}$ but I don't ...
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### Why does the power remain constant during the stepping up and stepping down of current in transformers?

I understand quite a bit of transformers, their structure and other concepts and formulas related to mutual induction. However I'm not able to explain why the electrical power has to be constant ...
662 views

### What's the point of an RMS value? [duplicate]

the RMS (root mean square) value of $f(x)$ is defined as: $$f(x)_{rms}=\sqrt{\frac{\int^b_a (f(x))^2dx}{b-a}}$$ Why do we do this very specific thing of taking the square, the mean, and then the ...
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### Motor's work and power against the gravity

Ok, I've read this answer: Why does holding something up cost energy while no work is being done? But more questions pop up. If there is no work being done does that mean that there is also no power ...
335 views

### Why does increasing voltage result in a decrease in current and not rather a decrease in power? [duplicate]

I recently read that in order to conduct electricity over vast distances via power lines they had to step up voltage which results in a decrease in current through the medium. This is reflected in the ...
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### Why do current carrying wires with smaller area heat up more than those with larger area?

Consider two wires of length $L$ and resistivity $\rho$, and consider a fixed voltage source with voltage $V$. The first wire has cross sectional area $A_1$ and the second wire has cross sectional ...
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### What is the meaning of power delivered by the battery after $t$ seconds?

I don't get it when a question asks power delivered by a battery after t seconds, are they talking about the total energy delivered by the battery in time t seconds divided by the time, or are they ...
31 views