# All Questions

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### hamiltonian in a rotating frame

ˆ H0 = h(ωopt − Gx)a†a + hΩb†b··· this is the hamiltonian of optomechanical system how this can be solve after switching to a frame rotating at the incomming frequency ωL.
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### Mass density of a cylinder increasing with the square of the radius

I’ve had to deal with a question like this on a test on friday and I just can’t get it out of my mind. I was supposed to calculate the moment of inertia of a cylinder with an inhomogenous yet ...
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### High School Physics-Electromagnetism

An insulated smooth square frame ABCD of side a is able to rotate about one of its side taken as positive axis. The plane is initially located at x-z plane. A magnetic field present in the region ...
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### magnetization curve for motors

I have query that if you observe magnetization graphs they are plotted between flux and armature induce voltage keeping speed constant but how does it happen ? Did every time to keep speed constant ...
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### Origin of time or origin of space-time?

This might be a mere theoretical concept and I might even get down voted for asking this. I read in several sources that winding back general relativity equations leads to $t=0$, origin of time. ...
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### Why move from Special Relativity to General Relativity? [on hold]

The concept of relativity is simple. Why take Maxwell's equations to a new Special Relativity level with the unproven assumption that photons have no mass? All other physical data (momentum, affected ...
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### Does “Schrodinger's cat” need entity knowledge to work?

I've never studied physics, but am interested in whether this paradox, from an interpretation of quantum mechanics, can still be stated if we don't know anything about unobservable entities. My ...
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### Pressure loss in an infinite pipe

I feel lost in this problem. I know pressure loss occurs in a pipe flow due to friction. Say given a constant diameter pipe, if we keep lengthening the pipe horizontally, and static pressure will ...
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### Speed of sound at phase transition — does percolation theory describe it?

I was discussing with a friend whether we expected liquid water or ice to have a higher speed of sound, near freezing; we figured it would be water since it was more dense. It turned out to be ice (by ...
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### basic question about work exercise

I am learning independently from Tobochnik's statistical physics text. He asks a warm up question about work: A person pushes a block up a frictionless ramp. Is the work positive, negative, ...
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### How can IR cameras see things colder than the camera?

I’ve read that only cold-blooded animals develop IR vision to spot warm prey because a mammal would blind himself with his own heat and not be able to see anything. But I’ve seen a FLIR camera, ...
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### Spectral covers and a specific exact short sequence

I have a question about the spectral cover construction of Friedman, Morgan, and Witten (typically used to map a description in heterotic string theory into F-theory). I realise this is a highly ...
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### Initial Velocity Question

What is the initial velocity vertically when a person jumps 0.5 metres into the air, neglecting horizontal movement. Is it just 0 m/s? And the final velocity would be -9.8m/s^2 * the time it took took ...
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### How much energy is released by decompressing water?

How much energy would be released if 2L of (relatively pure) water compressed to 1L at room temperature was suddenly decompressed to atmospheric pressure? Even a first-order approximation would be ...
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### Frequency range possible from a mechanical music box

Here is a small mechanical music box. The tines of a metal comb are tuned to emit a particular frequency when plucked. The material and structural characteristics of the comb, plucking cylinder, ...
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### If we harvest energy generated by Coriolis Effect of the earth, will the earth slow down?

Coriolis Effect causes strong winds in the upper atmosphere, and it's purely due to differences in the linear velocity of Earth's rotation across latitudes. Now the Earth is spinning with the energy ...
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### When we say particle in a box has quantized energy, is that kinetic or total energy?

In quantum mechanics, it is usually said that energy of the bound (constrained) systems such as particle in a box (infinite potential well) is quantized. It confuses me exactly what type of energy is ...
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### Motion in a Plane Velocity

If I were to throw a rock of a cliff at 12 m/s as a horizontal velocity, what will the final velocity of the rock become when it hits the ground? I am tempted to say 12 m/s because the horizontal ...
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### Action at a Distance

Since photons move at $c$, do they experience time or distance? If they don't, doesn't this explain action at a distance? From the point of view of the photons, there is no time, so the action at a ...
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### Could a strongly enough charged black hole allow for a strongly charged particle to escape the event horizon?

If there is a strongly charged black hole, and a particle with a strong charge of the same sign goes inside of the black hole's event horizon while moving quickly, is there a reason why it would not ...
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### Express state as eigenkets

This is very basic but I just suddenly got confused. Any state can be expressed as complete set of eigenkets with discrete eigenvalues: $$|P\rangle = \sum^n c_n |p_n\rangle$$ I understand the above. ...
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### Charge of electron in AC/DC circuit

If electrons in a DC circuit going through a metal wire carry only negative charge from negative to positive, then in a AC circuit through a wire does a electron carry both a negative charge and ...
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### Can neutrinos interact by the EM interaction and gravity?

A definition of a lepton is: A particle that does not interact by the strong force but does by the 3 other forces.$^1$ Neutrinos are leptons, so from the above definition one would expect it to ...