# All Questions

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### Force Problem: How long for car attached to massless frictionless pulley to move 20 cm?

I am stuck on a homework physics problem. The problem states: An initially resting 300g car is dragged along a horizontal frictionless table by a massless cord. The cord is attached to a vertically ...
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### Can the nonlinear hydrodynamic be ignored in the process of a ship leaning slowly？

Can the nonlinear hydrodynamic be ignored in the process of a ship leaning slowly， and the ship capsized ultimately. Thanks！
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### Negative charge on capacitor, Kirchoff differential equation with step function

I'm solving a differential equation of the form $$200q'+\frac{200}{3}q=3U_o-6U_6+3U_{12}$$ Where $U$ is the Heaviside step function. $q(0)=0 [Coulombs]$ After solving it, I get that at time $t=18$ ...
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### How is time real?

Isn't time a human created concept? I mean why hasn't anybody tread on the rationale that there's no time, only physical and chemical reactions which strive to react with each other at a different ...
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### What does it mean that quantum teleportation can be classically simulated?

Quoting here from Quantum Computation by Neilsen and Chuang : (Gottesman–Knill theorem) Suppose a quantum computation is performed which involves only the following elements: state preparations ...
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### Why do weak interactions give such slow decay rates, if the analog of the fine structure constant isn't signifigantly small?

Intuitively, it seems as though the reason would be a small value for the coupling constant, as the probability for emitting $W^{-}$ bosons would be low. However, it's value is almost the same as the ...
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### What makes Monocrystalline silicon a good semi-conductor? [on hold]

I'm researching Monocrystalline silicon for a school project and focusing on its application in Electronics. One area I'm researching is why the material is a good semiconductor, and what properties ...
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### Is a sonic boom loudest when source is at exactly Mach 1?

Please imagine this cartoonish thing: a flying loudspeaker, playing a continuous sound, with zero air resistance (i.e its moving through the air doesn't generate any whooshing sounds) is coming ...
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### What does one get when admitting negative mass? [duplicate]

So essentially, both gravitational and electric fields behave in exactly the same way. The only difference is that, while mass can only be positive, charge can be positive or negative. As I understand ...
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### Can this type of graph be analysed to produce any meaningful data?

The above is a graph of pendulum length on the x-axis measured in metres, and pendulum period on the y axis measured in seconds. The pendulum period is not squared. I know that if I square the ...
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### Why should Newton's third law necessarily be universal?

I read all the previous answers concerning the 3rd law and I have seen that it is definitely not universal. Newton derived his law from the collisions in a primitive 'cradle'. Why do physicists ...
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### What type of the charge particle were there at time of formation of the solar system according Nebular hypothesis.? [on hold]

When our solar system created by nebular hypothesis or any other theory. What type of the particle would be there? Charged particle? Are these accelerating or moving with high speed with different ...
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### How derivate paradox of dicressiang the charge in Liénard–Wiechert potential? [on hold]

My professor discuss the Liénard–Wiechert. and give the formula for the moving point charge. there was a paradox by which it charge density is replace by the charge with paradox times of decreasing ...
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### Does the lack of absurdities in our universe call into question the validity of multi verse theories? [on hold]

Does the lack of absurdities in our universe call into question the validity of multi verse theories? If the theories about multi verse are to be true and we have explained the immensely improbable ...
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### What is the physical interpretation of time-energy uncertainty? [duplicate]

I have a question. What is the physical interpretation of time-energy uncertainty?