# All Questions

140,265 questions
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### What are the Calculus that I needed in Classical Physics? Will I be having a difficulty? (See image of this thread)

As I am starting my class, I am wondering what is the math needed for my class “Classical Physics”. I was not given a bridging and my Baccalaureate course is Bachelor of Secondary Education Major in ...
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### Particle physics threshold energy

I read the article Threshold energy on Wikipedia about colliding particles and their threshold energy. Consider the case where a particle 1 with lab energy $E_1$ (momentum $p_1$) and mass $m_1$ ...
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### A block of mass 2kg is moving with a velocity of 2i-j+3k m/s. find the magnitude and direction of momentum of the block with the x-axis [on hold]

Please answer it. It is a question of momentum. a block of mass 2kg is moving with a velocity of 2i-j+3k m/s. find the magnitude and direction of momentum of the block with the x-axis
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### What stimulates pair production? [duplicate]

I read that it happens when passing a nucleus or an electron, but why does that cause pair production to take place?
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### What if there was no baryon-antibaryon asymmetry in our universe?

We know that the universe goes through different evolutionary phases: radiation, matter and later dark energy epoch. What would happen if there was no baryon-antibaryon asymmetry? How would the ...
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### Application in medical field

I have heard about many new developments in radiotherapy for treating cancer/tumors such as hadron therapy but why can't we use wave interference for it? Incoming waves could interfere destructively ...
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### Question on electric flux

In the first diagram(given below), the charge should not feel any force as the electric fields are not touching it. But now if we see the flux throw an imaginary cube, it will give out an electric ...
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### Charge density of infinite sheet of negative charge in presence of external charge

A tiny hole is made in an infinite, conducting sheet of charge. Assume initial charge density to be $-\sigma$. We put a positive charge $+q$ in this hole. Find the charge density of the sheet now as a ...
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### Thermal hysteresis and its physical significance in lipid membranes?

We usually associate the phenomenon of hysteresis with memory in the system. For example, magnetic hysteresis is the basis of hard disks(if I recall it correctly). There are also electronic circuits(...
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### A pendulum consists of a rod with length L and a coin of mass m

A pendulum consists of a rod with length $L$ and a coin of mass $m$. The pendulum is held in a horizontal position and then is released with a minimum velocity needed to make a full circle. What'...
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### How much amount of induction should occur?

Consider a conductor placed in a constant external electric field. Electrons within the conductor redistribute themselves till the internal electrical field (due to polarization of charge) will equal ...
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### The spring paradox: Is there any rational transformation for the relativistic force?

A simple thought experiment crossed my mind a few years ago for which I could not as yet find a convincing answer: Assume that a mass-less spring $S_1$ with (proper) constant $k_0$ hangs from the ...
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### Why do we use a cylinder as a Gaussian surface for infinitely long charged wire?

Why do we use a cylinder as a Gaussian surface for infinitely long charged wire and not some other shape like cube?
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### What is this text talking about (about change of spacetime co-ordinate systems)?

I'm completely lost on the last paragraph. What expanding sphere thing are they talking about? I have no idea. Can someone explain this text part by part?
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### How can beta plus decay be possible?

$\beta +$ decay is where a proton gets turned into a neutron and a positron and a neutrino. However, a neutron is heavier than a proton, so obviously this reaction is endothermic. So then, why does ...
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### Electric current dipole moment

Electrical Current Dipole of dipole moment $\mathbf{p_{EC}}$ has unit of $A\cdot m$. My knowledge of dipole moments unfortunately stopped in high school where I learned that dipole moment $\mathbf{p}$ ...
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### Fermi level in metals and semicoductors

As we read about Fermi energy, it is the energy of the highest occupied electrons. But if we look at the energy level diagram of semiconductor the Fermi level is situated somewhere between the valence ...
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### Conductance Charged Box

A box with thick and conductive sides with dimensions: Lx, Ly, Lz- while LZ>>Lx,Ly. The long dimension of the box [Lz] can be viewed as infinite so Phi(x,y,z)=Phi(x,y) Given that: Phi(0,y)=-Phi(Lx,...
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### Radius vs speed for flywheel energy storage

If I understand the formula correctly, the equation for kinetic energy of a flywheel is $mw^2r^2$ whereas the formula for "centrifugal force" is $mw^2r$. So how come so much focus is on the speed of ...
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### Writing a two variable function$f(x,t)$ in terms of Dirac-Delta $δ(x)$ function and a function $P(t)$?

How to write a two variable function $f(x,t)$ in terms of Dirac-Delta $\delta(x)$ function and a function $P(t)$? For example; I read something in a book. You can find the following picture. But ...
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### My new equation of motion is right or wrong [on hold]

Every equation includes acceleration, but form the three equations I made forth equation of motion.![enter image description here](https://i.stack.imgur.com/IUrcH.
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### Why there are three reactions at fixed beam in F.B.D?

It is fixed so no reactions will be present, then how three reactions at fixed beam in F.B.D? In F.B.D, we draw two reactions and moment reaction at fixed beam: Why there are three reactions at ...
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### Why is effective mass a tensor?

So I came across the effective mass concept for solids the other day. It was mentioned that the effective mass is a tensor and may have different values in different directions. However, this is stark ...
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### How will a polar molecule affect another molecule nearby, why it feels a relatively large force?

Mean position of the negative charges and positive changes are not at the same point (polar molecule) how will that affect another molecule nearby, why it feels a relatively large force? Will the type ...
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### Is friction a conservative force when a ball rolls down an inclined plane(pure rolling)?

My book says friction is non dissipative for a cylinder rolling down an inclined plane,so is it conserved?
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### Nuclear Physics Question

How could I calculate the chance of a proton actually joining the nucleus and 2 protons and 3 and so on? Assuming a large number of protons are fired at a substance?
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### How small does a hole in a cup have to be to hold water without dripping? [duplicate]

I am creating a drain that lets water in but keeps pieces of plastic out. I need to know the size of a standard water droplet.
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### In Feynman lecture Vol1. chapter12 about friction, $F = μN$ will fail because of the excessive heat generated. Why is that?

$F = μN$ will fail because of the excessive heat generated if the normal force or the speed of motion gets too big. Why is that? "$F = μN$, where μ is called the coefficient of friction (Fig. 12-1)....
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### Oscillating spring, speed close to the equilibrium: How is this answer not 1.5? [on hold]

I have this question with the answer listed as $2.0\,\mathrm{m/s}$. "A $1.25\,\mathrm{kg}$ mass on a spring with a constant of $12.0\,\mathrm{N/m}$ is oscillating back and forth. Its maximum ...
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