# All Questions

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### defining axes for conservation of energy

The question follows my working for reference. If only conservative forces apply in the closed system then $$E_i = E_f$$ $$\Rightarrow (U_s + U_g + K)_i = (U_s + U_g + K)_f$$ And at the points ...
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### Is work done by how much velocity is changed or how much displacement is done?

A sailboat is moving at a constant velocity. Is work being done by a net external force acting on the boat? The answer key is "No" according to the work energy theorem about work is done when ...
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### Connection to spin 1/2 electron system?

In another Physics stack exchange thread here, Spin matrix for various spacetime fields I obtained the generator of rotations of the SO(2) rotation group for an infinitesimal rotation of 2D vectors. ...
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### can we get electrical energy from gravitational energy? [duplicate]

Now I'm trying to give an answer of the question. Satellite rotates about earth by the gravitational force of earth. Now if we place the satellite in such an orbit so that it rotate in opposite to ...
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### Help with deriving an asymptotic expression

Note: I don't know if this is the best place for this question, because it is very specific. However, I'm not sure of a better place to go (apart from one of the other SE's). If you have a ...
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### Macro-Level Explanation of Fluid Heat Transfer

Here's something I've been struggling with for a while. Say you have a hot fluid and cold surface (or the reverse, so long as there is a temperature difference) where the fluid flows over the ...
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### Propagation of light from a point source in seawater [on hold]

If the light intensity of a point source (480 nm) is 1.09 x 10-8 Wm-2 at a distance of 1 m, what would that intensity be at a distance of 0.005 m in seawater? I have used the Beer-Lambert Law to back ...
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### How to derive equation for probability current density in relativistic quantum mechanics [on hold]

How does one derive equation for probability current density in relativistic quantum mechanics? I am asking for textbook-styled explicit derivation. No need for any other background knowledge.
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### Which experiment would be able to detect change in the speed of light? [duplicate]

Since the unit of distance is defined in terms of speed of light in vacuum, if the speed of light in vacuum were to change by "magic", what experiment would be able to detect that? Is there a theory ...
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### Relative acceleration pulley

Considering If we have pulley with strings on both sides giving different velocities to them, we know velocities of points between them, on diameter, as velocity vector is tangent to it, just ...
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### How do inflationary models predict the generation of gravitational waves during the inflationary period?

Recent results from the BICEP2 experiment have produced a lot of talk about the primordial gravitational waves produced during the inflationary period. I would like to have some explanation about how ...
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### Just a contraction of indices

I came across a contraction which is not giving the desired result. This is a toy problem in how to get a supergravity theory in low energy limit of a superstring theory using the vanishing of beta ...
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### How to calculate the 2-point funtion of gravitons?

I'm curious about how to calculate the 2-point function of graviton, but there are no textbooks of general relativity covering this problem. So how to calculate it? In which book can I find the ...