# All Questions

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### Why isn't momentum conserved in this pulley problem?

I have some conceptual doubt about method of solving this problem. 24. A block of mass $m$ and a pan of equal mass are connected by a string going over a smooth light pulley as shown in figure ...
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### Regarding synchronization of clocks in special relativity

I am trying to read of synchronization of two clocks in same inertial frame in special relativity. Suppose we have two synchronized clocks in an inertial frame placed at positions $x_1$ and $x_2$ in ...
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### Why do people wear black in the Middle East?

I have read various dubious explanations as to why people often wear black in the heat, from cultural to somehow encouraging the evaporation of sweat (unconvincing). So, does anyone know what, if any ...
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### All possible photons wavelengths

As far as I know all photons come from electrons loosing their energy. I remember from physics and chemistry classes, that electron can loose or get only certain determined amount of energy. Also I ...
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### Phonon spectrum

I had a question regarding phonon spectrum in condensed matter. Consider a cubic lattice with '$p$' atoms per primitive cell. Consider the lattice plane used for derivation of the phonon spectrum to ...
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### Would neutronium emit heat?

Since accelerating a charge creates EM radiation, and there are no charges in neutrons to be accelerated, would that mean neutronium emits no radiation? Consequently, to preserve the second law of ...
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### Why would an alpha-beryllium neutron source generating a radioisotope not produce controllable net power?

I have a question. I was looking through the table of nuclides and noticed that the energy needed to produce certain radioisotopes was less than the energy given off by the radioactive decay of that ...
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### Is it theoretically possible to prevent or deter a star from becoming a black hole?

Suppose NASA decides too many black holes are being produced in a year, so it decides to do something about that. Given our current scientific knowledge, is there theoretically any way NASA could ...
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### Allowed Virtual Displacements

I am having trouble understanding the kinds of virtual displacements which are permitted for a given constrained system. I have a specific example in mind: A block of wood resting on a table parallel ...
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### Why can we see through rain?

I am gazing through my office window into a heavy rain. I am thinking that raindrops are like small lenses that bend the light. Thus I am surprised, that I can clearly see other buildings through the ...