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Results tagged with conservation-laws
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user 282830
The statement that a property of a system does not change if the system is isolated.
1
vote
Time spent by a comet inside the Earth's orbital (Kepler problem re-visit)
I try to work it out following the clues from G.Smith for a complete record.
in 2-d polar coordinate, the velocity $\vec{v}$
$$
\vec{v} = \dot{r} \hat{r} + r \dot{\theta} \hat{\theta} = v_r \hat{r …
- 4,314
3
votes
2
answers
1k
views
Time spent by a comet inside the Earth's orbital (Kepler problem re-visit)
I come across this interesting problem comet-x-earth. It was an exam problem asking the time that a comet will be spent inside the Earth's orbital. I make an illustration for the problem:
The comet i …
- 4,314
3
votes
Accepted
Infinitesimals meaning in this context
The notation $M(dt)$ or $v(dt)$ is not acceptable. Typical notations are like:
At the time $t$:
mass of rocket $M(t)$
velocity of rocket $\vec{v}(t)$
Then at the time $t+dt$
mass of rocket $M(t+dt …
- 4,314
0
votes
Why is angular momentum conserved in a central field?
Your reasoning about the angular momentums is corrrect. What is needed is an interpretation: note that $\frac{d\vec{L}}{dt} = \vec{\tau}$, and both $\vec{L}$ and $\vec{\tau}$ are dependent on the cho …
- 4,314
2
votes
Accepted
Conservation of angular momentum of disk and block
A conceptual error: The parallel axis theorem is used to find the inertial moment about an rotating axis which is not the CM. In this problem, the disk is not rotating about the CM (for rock and disc …
- 4,314