Questions tagged [power]

The time rate of change of energy

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1k views

How to find power required for rotating blades given the required shear cutting force [closed]

I want to design a sugar cane bud cutting machine. The rotating blades are connected to the output shaft of a speed reduction box ($30\,{\rm rpm}$). The shear force required for cutting is $1200\,{\rm ...
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1k 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 $$W=\frac{P}{1s}=...
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2answers
554 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. These ...
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4k 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 $B$ ...
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1answer
61 views

Is watt unit depended on turbine speed

Is watt unit depended on speed of turbine? I think, if turbine rotates more speed it will produce more watts. Is it right?
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3answers
10k views

Different formulas for calculating power [duplicate]

$P=IV$, $P=I^2R$, $P=\frac{V^2}{R}$, what are the distinctions between these equations? How do you know which equation to use when?
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1answer
377 views

Can magnetic energy be used to create a magnetic motor which can power vehicles and machines? [closed]

Can magnetic energy be used to create a magnetic motor which can power vehicles and machines?
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3answers
2k views

Power of a runner

How can someone calculate the power in watt that a runner produces, when he runs uphill and downhill? Is there any algorithm? It is important to take under consideration the uphill and downhill ...
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0answers
46 views

Electric Power ($I=V/R$ vs. $I=P/V$) [closed]

I have a homework question that goes: "A power station delivers $750$ kW of power at $12,000$ V to a factory through wires with total resistance $3.0$ Ohms. How much less power is wasted if the ...
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0answers
40 views

Instantaneous power: is it meaningful? [closed]

I've recently started questioning whether instanteous power is a useful concept in mechanics. For point masses, let's define it as $P(t)=\mathbf{F}(t) \cdot \mathbf{v}(t)$. Then, we can define work${}^...
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2answers
329 views

Power in Series and Parallel circuits

My textbooks states that the brightness of a light bulb that is connected in a circuit is determined by its power. That is, a light bulb connected in series would be brighter if it has a higher ...
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1answer
118 views

Calculating power with force as a function of time [closed]

While doing an AP question in Physics C today I answered the question differently from the professor but I'm not sure what part of my reasoning is incorrect. A $100\ \rm{kg}$ block is being pulled ...
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1answer
43 views

Photon energy and power

My question has to do with the solar spectrum. I understand sunlight is composed of light of different wavelegnths, and these wavelegnths have different energies associated with them. I also ...
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2answers
3k views

Can power (in the context of work and energy) ever be negative?

Consider this question which HAS definitely been asked but i ask you now to question your first inclination to just 'do the question' and explain the thought process. Restrictions: assume you only ...
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1answer
273 views

Work, Energy, and Power- Hooke's Law & graphing

The purpose of the work, energy, and power lab is to demonstrate the validity of Hookes Law over a limited range of displacements, measure the spring constant of several springs, and determine the ...
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2answers
54 views

Energy Creation Using Water, Generators, and a Pump

So a friend and I are arguing over an infinite energy idea that he had about using gravity, that is an almost infinite source of energy. Water to use to push a generator by dropping and hitting the ...
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1answer
28 views

Why is the power for an object of mass m moving at a higher velocity greater than that for the same object moving at a lower velocity?

I understand the equation Fv but I will like a more intuitive answer concerning why the rate at which energy is transferred must be greater
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1answer
122 views

Impact force of a pillow?

My friend and I just had a discussion about how dangerous it would be to get hit in the face with a pillow thrown out of a train. If we say the train is traveling at 100km/h and the pillows weight is ...
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1answer
2k views

How can power factor be improved by using a capacitor in an LCR circuit?

First of all what is even meant by improving power factor? My book says we can improve power factor by making impedance tend to resistance I.e. Z-》R, and then they say that power factor is improved by ...
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2answers
974 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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2answers
67 views

An electric bulb is rated 220 V and 100 W. When it is operated on 110 V the power consumed will be- [closed]

An electric bulb is rated 220 V and 100 W. When it is operated on 110 V what will be the power consumed? The answer to the question is 25 W using the formula P=V^2/R. But if I use the formula P=VI I ...
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1answer
535 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
52 views

An engines power is 650kW and the shuttle's speed increases from 120 m/s to 160 m/s in t seconds [closed]

note sure if I'm missing something obvious, but i cant seem to find a good way to tackle this question. A space shuttel of mass 400kg is moving in a straight line where there is no resistance. the ...
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3answers
65 views

Could a vacuum provide exponential power?

A vacuum requires little power to be created and when spread over a large surface area can lift thousands of pounds. Is there a way to generate enough work out of this to create more power than was ...
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2answers
10k views

What is the relationship between power and energy? [duplicate]

What is the relationship between power and energy? Of course, this is a very basic and fundamental question, but it's one that many people learning physics struggle with. I'm asking this to have a ...
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1answer
2k views

If a 2,400 lb. car is moving at 1 mile per hour, how much force is required to stop its motion? [closed]

Given that I stand behind or in front of a car and someone will move the car from within at approximately 1 M.P.H., how much force is needed to stop the force driven by the engine to put the car at ...
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3answers
165 views

Electric Current Power Calculations [closed]

With regards to the equations: $P=VI$ ; $P=V^2/R$ and $P=I^2R$, if you are given $P$, $V$, $I$ and $R$ for a circuit, how do you know which equation to use? Does the use of an equation have to do ...
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2answers
386 views

AC vs DC & why we ended up using AC for power in our homes, etc [duplicate]

I think that DC is better than AC (and yes I do have a reason, check the comments). Also, if it (DC) is in-fact better than AC why did we use AC then?
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2answers
166 views

Why we say that electrical energy is power over time p x t? [closed]

How electrical energy can be power over time when electrical energy is actually potential energy? from a lot of sources (wiki ,study.com..) comes the information that electric energy is potential or ...
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2answers
163 views

Why isn't work a logical quantity? [duplicate]

Please read till the end, before you answer. I'll start off with the examples to get to the point. Drop a block from 1 meter and it will have speed v when it reaches the ground, with total work ...
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1answer
67 views

Is it possible to create usable light from magma?

Say you drilled a hole down to the magma layer. Hot lava emits light. From what I've seen lava is red(?) hot. Then if you put some fibre optic cables down into the magma layer maybe protected at the ...
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2answers
218 views

Why does Work Done Appear to be More than 100% Energy in a System? [closed]

Energy is equivalent to the work done on a motor. The work done on the motor is multiplied by more than 100% by recycling the energy the motor uses. Why then does the energy in the system appear to be ...
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1answer
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Calculating energy needed for by a car climbing a slope [closed]

I'm having a difficult time answering this question. I think I'm just converting the units wrong somewhere: You're the CEO of a courier company, and you decide to select an electric car for your ...
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1answer
144 views

How is power defined?

Isn't power defined by: $$P=\frac{dE}{dt}$$ (?) I see in all websites that power is the amount of work done per time. Is it represented only like this? Why?
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1answer
666 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 ...
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1answer
109 views

Can a fusion bomb make electricity? [closed]

Would blast energy remove a single piece of pre-cut earth above an underground explosive? Could you then break apart the piece of earth and lower it back into the cavity as a way of generating power? ...
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2answers
18k 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?
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1answer
478 views

Work, energy and power [closed]

A load of mass $m$ slides down a smooth plane with inclination title from point $A$ to $B$. The same mass is then dropped from $A$ to $C$. Could anyone decipher this $\downarrow$. I've edited the ...
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1answer
59 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
211 views

Temperature of 100w bulb [duplicate]

What is the running temperature of a 100w bulb if it's resistance while on is 50 ohms and the mains voltage is 240 V RMS.
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1answer
2k views

Why Ohm's law is followed inside the house? [closed]

In power transmission lines, as power remains constant, according to $P=VI$, current decreases when voltage increases, thus Ohm's law is not followed. But inside our house current increases when ...
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1answer
224 views

Could an infinite spinning windmill create endless electricity? [closed]

This is not so much a question about if this idea is physically possibly, but more a question of if it was possible. If a magnet could somehow push a windmill around at a constant speed continuously, ...
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3answers
2k views

Relation between power & thickness of the filament [closed]

Tell me what relationship is used to solve the question given below. There are three bulbs of power 60, 100 and 20; which one has thickest filament for same source? (a) 100 (b) 20 (c) 60 ...

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