What are the different death scenarios for a black hole? I know they can evaporate through Hawking radiation - but is there any other way? What if you just kept shoveling more and more mass and energy into the black hole?

Is there any reason to believe that any measure of loudness (e.g. sound pressure) might have an upper boundary, similar to upper limit (c) of the speed of mass?

A bicyclist makes a trip that consists of three parts, each in the same direction (due north) along a straight road. During the first part, she rides for 27.8 minutes at an average speed of 6.13 m/s. During the second part, she rides for 44.7 minutes at an average speed of 3.16 m/s. Finally, during the third part, she rides for 8.19 minutes at an average speed of 19.7 m/s. (a) How far has the bicyclist traveled during the entire trip? (b) What is the average speed of the bicyclist for the trip?

It's a Christmas time and so I hope I'll be pardoned for asking a question which probably doesn't make much sense :-)

In standard undergraduate nuclear physics course one learns about models such as Liquid Drop model and Shell model that explain some properties of nucleus.

But as I understand it these models are purely empirical and most importantly incompatible. Perhaps it's just my weak classical mind but I can't imagine same object being described as a liquid with nucleons being the constituent particles floating freely all around the nucleus and on the other hand a shell model where nucleons occupy discrete energy levels and are separated from each other.

Now I wonder whether these empirical models are really all we've got or whether there are some more precise models. I guess one can't really compute the shape of the nucleus from the first principles as one can do with hydrogen atom in QM. Especially since first principles here probably means starting with QCD (or at least nucleons exchanging pions, but that is still QFT). But I hope there has been at least some progress since the old empirical models. So we come to my questions:

Do we have a better model for description of a nucleus than the ones mentioned?

How would some nuclei (both small and large) qualitatively look in such a better model? Look here means that whether enough is known so that I could imagine nucleus in the same way as I can imagine an atom (i.e. hard nucleus and electrons orbiting around it on various orbitals).

What is the current state of first-principles QCD computations of the nucleus?

Theory predicts that uniform acceleration leads to experiencing thermal radiation (so called Fulling Davies Unruh radiation), associated with the appearance of an event horizon. For non uniform but unidirectional acceleration the shape of the experienced radiation changes from thermal to other spectral densities, but also is predicted to exist. But suppose the acceleration is periodic and oscillatory, i.e. no permanent horizon persists? In particular, what about the case of harmonic motion, for a full cycle, half a cycle, etc.?

Here is an even simpler related problem that makes the apparent paradox easier to see. Suppose at proper time t=0, I accelerate at constant acceleration k in the x direction for t0 seconds, presumably experiencing Unruh radiation. Then I accelerate with acceleration -k, (in the -x direction,) for 2*t0 seconds, seeing more Unruh radiation coming from the opposite direction, and then I finish with with acceleration +k for the final t0 seconds. At the end of the 4*t0 proper seconds, I'm back where I started, at rest, without any event horizon. Was the Unruh radiation I felt when reversing acceleration secretly correlated or entangled with the radiation I initially and finally saw? Otherwise, from a more macro scale, I didn't actually necessarily move much, and the acceleration event horizon was instantaneous, evanescent and fleeting, so whence arose the Unruh radiation?

I was told that the Galilean relative velocity rule does not apply to the speed of light. No matter how fast two objects are moving, the speed of light will remain same for both of them.

How and why is this possible?

Also, why can't anything travel faster than light?

A wheel of radius b is rolling along a muddy road with a speed v. Particles of mud attached to the wheel are being continuously thrown off from all points of the wheel. If v2 > 2bg, where g is the acceleration of gravity, find the maximum height above the road attained by the mud, H = H(b,v,g).

I heard somewhere that quarks have a property called 'colour' - what does this mean?

I am trying to get a common understanding from these two previous questions:

Why does the mass of an object increase when its speed approaches that of light?
What happens if light/particles exceeded the speed of light for a particular medium (sic)

Does the increase of mass occur only if the particle approaches c (speed of light in a vacuum) or if it simply approaches the speed of light in its current medium? For example, does the mass of charged particles increase during Cherenkov radiation?

The nose of an ultralight plane is pointed south, and its airspeed indicator shows 39m/s . The plane is in a 12m/s wind blowing toward the southwest relative to the earth.

Question A:

Letting x be east and y be north, find the components of v? P/E (the velocity of the plane relative to the earth).

Question B:

Find the magnitude of v? P/E.

Question C:

Find the direction of v? P/E.

Any help is appreciated!

Three identical point charges of charge q = 5 uC are placed at the vertices (corners) of an equilateral triangle. If the side of triangle is a = 3.3m, what is the magnitude, in N/C, of the electric field at the point P in one of the sides of the triangle midway between two of the charges?

Yesterday I looked underwater with my eyes open (and no goggles) and I realized I can't see anything clearly. Everything looks very, very blurry. My guess is that the eye needs direct contact with air in order to work properly. With water, the refraction index is different, and the eye lens are not able to compensate for correct focalization on the retina.

Am I right ? If so, what lenses should one wear in order to see clearly while under water ?

Two equally charged particles, held 4.2 x 10^-3 m apart, are released from rest. The initial acceleration of the first particle is observed to be 7.4 m/s² and that of the second to be 11 m/s². If the mass of the first particle is 5.9 x 10^-7 kg, what are (a) the mass of the second particle and (b) the magnitude of the charge (in C) of each particle?

Decoherence times can be estimated and are inverse functions of mass. Since there are no upper bounds on mass, can decoherence time be shorter than Planck time?

Initially Wheeler and Feynman postulated that, the electromagnetic field is just a set of bookkeeping variables required in a Hamiltonian description. This is very neat because makes the point of divergent vacuum energy a moot point (i.e: an example of asking the wrong question)

However, a few years later (1951), Feynman wrote to Wheeler that this approach would not be able to explain vacuum polarization.

Anyone knows what was the argument for saying so? I don't see how allowing both processes with entry and exit particles and processes that begin in pair-creation and end in pair-annihilation makes the existence of a field a requirement.