Questions tagged [momentum]

In introductory mechanics, the momentum of a particle is its mass times its velocity. In electrodynamics, the momentum of a field is proportional to the cross-product of the electric field with the magnetic field. In special relativity, momentum is generalized to four-momentum.

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Doesn't universe violates law of conservation of linear momentum?

As mass of universe is not constant,it means that its linear momentum is not constant.But thinking in another way,is universe subjected to a net external force?But what is external for universe?...
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Does linear momentum of a hydrogen atom-system remain constant during electronic transitions?

When electronic transitions(excited to ground) take place in a hydrogen atom, does the linear momentum of proton-electron system remain constant?
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Proof that the momentum operator is hermitian without assuming the wavefunction approaches zero at infinity?

I am currently taking my second semester of quantum mechanics. For a number of proofs in the course, we have used the assumption that the wavefunction goes to zero at infinity. We have simply used the ...
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Proof that $v=\frac{dE}{dp}$ at relativistic speeds?

This is a formula I have seen stated in two different places in a relativistic context, but I do not know the proof and seem unable to derive it on my own. $E$ is the energy of a free particle, $v$ is ...
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A ball of mass $m$ is dropped from a height $h$ on to a rigid floor. If $e$ is the coefficient of restitution [on hold]

A ball of mass 'm' is dropped from a height 'h' on to a rigid floor. If e is the coefficient of restitution, the time required for the complete bounce is? After finding the initial and final velocity ...
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How to find the acceleration of two blocks? [on hold]

Help I'm really lost. I'm not even sure what forumla im supposed to be using on this problem A 15 kg block is placed on top of a 25 kg block (see figure below). A force of 387 N is applied to the ...
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Is the coefficient of restitution always equal to the square root of the ratio of final kinetic energy to the initial kinetic energy?

The coefficient of restitution (COR) according to some sources (https://en.wikipedia.org/wiki/Coefficient_of_restitution) is equal to the square root of the ratio of final kinetic energy to the ...
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Why is the momentum always conserved in elastic collision?

As the title above, why is the momentum always conserved in elastic collision (no loss of kinetic energy)? Does it related to the conservation of kinetic energy? If so, how do we prove that? Further ...
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How do we calculate the force applied by a ball on a wall which bounces back? [on hold]

If we have a ball which we throw toward a wall which touches the wall and bounces back then how will you calculate the force applied by the wall on the ball because the the contact time of the ball ...
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Is it Valid to Derive $E = pc$ From the Energy-Momentum Relationship for Photons?

Given a particle with mass $m$ moving at velocity $v$, total energy is: $$E^2 = (pc)^2 + (mc^2)^2$$ Note I am not using the relativistic - rest mass convention, as I was taught to think in ...
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Newton's Third Law of Motion? [duplicate]

Newton's third law of motion states that every action has an equal and opposite reaction. But, on punching a wall, I feel much greater force than on punching an inflated balloon. So, what does it mean?...
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Sign of stress tensor in momentum conservation equation

I have a confusion and would be grateful if anybody could help clear it up. So I was reading Kip Thorne's modern classical physics and came up on the following definition of stress tensor: $T_{ij}$ ...
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Discussion regarding work done? [closed]

Suppose I take a box with some masses and pull it along the table at a constant speed. In this case, there is a force pulling to the right (the string) and a frictional force pulling to the left. ...
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Is the field-momentum operator ambiguous?

In this question I asked wether the definition of the momentum operator as an operator that has to generate translations by satisfying the canonical commutation relations was ambiguous. The answer to ...
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The impulse on a wall

If a ball was thrown to a wall, How could we calculate the impulse on the wall ? For example, if I throw a $2kg$ ball with $4m/s$, and it returned with the same speed but in the opposite direction, ...
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Should a wavefunction in momentum space be normalisable?

Is this a condition that the wavefunction in momentum space should be normalizable? Like we said that a particle has to be between ${-\infty}$ to ${\infty}$. Will the same argument also work for ...
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Will the rods rotate about the hinge after collision?

The problem is like this: two blocks(considered to be point masses) of masses $m$ are simultaneously moving with uniform velocities $v_0$ towards the rods and they hit the edges of rod and stick to it(...
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How to show that translational invariance in $y$ of implies that it's an eigenstate of $p_y$?

Let us consider a particle on a plane with uniform magnetic field $B=B\hat{z}$, and hence with the Hamiltonian $H=\frac{1}{2m}(\vec{p}+e\vec{A})^2$. I am concerned with finding the energy eigenstates, ...
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Is the change in momentum of each object in a collision the same?

I have this question concerned with collisions In the solutions, they work out the change in momentum of the blue car, which comes to 0.048. I also calculated the change in momentum of the red car 0....
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