# Tagged Questions

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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### What happens if object is thrown in empty space?

If I throw a object in empty space, I apply a force to throw that. Then it gains some acceleration and it's speed increases. So will it's speed keep on increasing, or it will get stable? If yes, ...
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### When momentum coincides with impulse

If an object is pushed for some time by some force from a resting state, can I say that at the exact moment the force is removed, impulse equals momentum?
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### Is there such a thing as instantly stopping?

I'm sorry if this is a stupid question, but I've never taken a physics class and I was curious about something. But anyway, my question is, is there such a thing as instantly stopping? For example, if ...
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### Change in momentum in a photon collision?

Let's say I drop a ball on the ground and it bounces up. According to classical physics, once the ball hits the ground it goes trough a short phase of deceleration until the velocity reaches zero, ...
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### Ball collides with another. Find velocities [closed]

A ball moving at a velocity of 5.0 m/s east when it collided with an identical ball at rest. Both balls are the same mass. The first ball moved at 60 degrees north of east. The second went 30 ...
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In the section of 'The free particle' in 'Introduction to quantum mechanics, second edition' by Griffiths page 65. He has the wave equation as $$\Psi(x,t) = \frac{1}{\sqrt{2 \pi}} \int_{-\infty}^{\... 3answers 102 views ### How does commutation between the hamiltonian and angular momentum operator (squared) imply conservation of Angular momentum? So we are looking at central potentials in QM; The lecturer poses the question, when is \textbf{L} conserved? He then considers the commutator of \hat{H} and \hat{L^2}. We have;$$\hat{H}=-\...
Simple Question , Consider two objects namely $A$ and $B$ where $B$ is stationary and $A$ is moving towards $B$ with velocity $v$. When the two objects touch each other what does actually happen ...