# Tagged Questions

Energy is the conserved quantity associated to time-translation invariance and represents the work a system is capable of doing. Use this tag for questions about energy, and consider adding [tag:energy-conservation] if it is specifically about its conservation.

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### How much energy is consumed by a aircraft to maintain a speed of sound? [closed]

Let's assume that the aircraft is 1000kg and it is flying in a air density of 1.225kg/m^3 at the speed of sound in air. Just how much energy does it require per second to maintain flying at this ...
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### Kinetic energy of a rotating rod [closed]

I have no idea where to even begin with this... Find the kinetic energy of a record of uniform density, mass 50 gm and radius 10 cm rotating at 33 and 1/3 revolutions per minute. Normally I would do:...
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### Is it necessary to consume energy to perform computation?

As far as I know, today most of the computers are made from semiconductor devices, so the energy consumed all turns into the heat emitted into space. But I wonder, is it necessary to consume energy ...
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### What do I need to know to calculate the price per km for plug-in hybrid or electric cars? [closed]

Knowing the per kWh price of electricity, what other factors are needed to calculate how much would one pay per km traveled on electric power compared to gasoline power? EDIT: For example, the ...
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### How is energy extracted from fusion?

I understand that combining deuterium and tritium will form helium and a neutron. There are three methods to do this (1) tokamak (2) lasers and (3) cold fusion. I would like to know after helium is ...
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### Does ABS shorten stopping distance of a car?

ABS, from German Antiblockiersystem, is a device put in almost every new automobile. The web has lots of explanations about the system, how it works, but I don't understand how it shortens the way of ...
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### Potential and Kinetic Energy

In engineering school you learn the basic swing problem. Essentially that there is a transfer of kinetic energy (as seen in the velocity at the bottom of as swing) to potential energy at the top of ...
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### From where do the permanent magnets get energy from? [duplicate]

I have a doubt about permanent magnets. If a magnet is permanent it can attract some materials permanently. Attracting something involves energy. If a permanent magnet can do this forever, from where ...
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### force applied not on the center of mass

When applying a force outside of the center of mass of the body, the body will get both linear and angular momentum. Right? Does the linear velocity from this force equal to the linear velocity from ...