# Questions tagged [power]

The time rate of change of energy

71 questions
Filter by
Sorted by
Tagged with
456 views

### High Voltage Powerlines - clarification of energy loss

I've been having a bit of trouble understanding the High-Voltage powerlines. If I was sending power from $A \rightarrow B$, we have: Ohm's law $V = IR$ Power lost in the form of heat $P = I^2 R$ ...
359 views

### Why isn't the product rule used in the definition of mechanical work?

Mechanical power is normally defined as $P = \mathrm{d}W/\mathrm{d}t$, and work is normally defined as $W = \vec F \cdot \vec x$. Today an undergrad pointed out a confusion he had from Griffiths' E&...
3k views

7k views

### Does the 'mAh' rating of a battery have something to do with its power?

I'm curious about the 'mAh' of a battery: how can this impact the power of the battery? I've done some research on the internet, and most of the articles I found explain about the 'amount of charge ...
617 views

### How to inject the maximum acoustic power into a block of granite?

I know that we can use transducers that are glued to a surface to achieve this. If I want, for example, to have 200 watts of actual acoustic power in the audible range in the granite, is a transducer ...
17k views

### Why is power dissipated in a circuit maximum when external resistance is equal to the internal resistance in the circuit? [closed]

[![question 24]]Suppose in a circuit the battery has emf 6V and internal resistance 3ohm. It is connected to an external resistance = R ohm. According to my ...
265 views

### Power vs. Speed - Indoor rowing

In the sport of indoor rowing (and probably others) I know that to double your speed you must increase your power output by a factor of eight. I am wondering why this is the case. The indoor rower ...
479 views

### Does a rocket engine apply more power as the rocket's speed increases? [duplicate]

To clarify my level of knowledge, I'm a high school student all the way through AP Physics C: Mechanics. So, let's imagine that there is a rocket travelling through the vacuum of space (ignoring ...
261 views

### Power of water pump

Consider a water pump pushing water through a pipe: We wish to find the energy which the water pump has to expend to keep the water flowing through the pipe. Writing Newton's second law for water ...
10k views

### Calculating the mechanical power of a water pump

Say I want to pump water from one container to another. The water levels are 3 meters apart, and I want to pump 10 litres per hour. I figure the mechanical power necessary, assuming no losses, is:  ...
1k 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.
503 views

### infinite power from constant force?

P = W/t = Fd/t = Fv So, if we keep exerting a small constant force and the velocity keeps increasing to near infinite, we should be able to get near-infinite power from the small constant force. We ...
### Difference between $I^2R$ and $V^2/R$ and $VI$ for measuring power $P$
We use $I^2R$ or $V^2/R$ or $VI$ for measuring power $P$. Are all of these applicable for all circuits? I have seen in some circuit $V^2/R$ is not equal to $I^2R$. Why is that?