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Applies to questions of primarily educational value - not only questions that arise from actual homework assignments, but any question where it is preferable to guide the asker to the answer rather than giving it away outright. Please READ THE GUIDANCE IN META before asking homework-like questions.
2
votes
Accepted
Angular momentum of the electric field of a point-like electric charge and the magnetic fiel...
Answer expected by following author's hints.
\begin{align}
\mathbf{L}_{eg} &= \dfrac{1}{4\pi}\int \mathbf{r'} \times \left [\mathbf{E} \times \mathbf{B} \right] d^3r'\\
& = \dfrac{1}{4\pi} \int \left …
2
votes
1
answer
2k
views
Angular momentum of the electric field of a point-like electric charge and the magnetic fiel...
I am currently reading "Magnetic Monopoles" of Ya. Shnir. My problem is I can not retrieve a result the author provides in the first chapter of the first part. In this chapter, he studies the non-rela …
1
vote
How is the uniform gravitational field approximation $F_g\approx mg$ near Earth's surface de...
The equation
$$\ddot{r} = -\mathbf{g},$$
is valid iff $\dfrac{h}{R_e} <<1$. The gravitational force is :
$$\mathbf{F} = -m\dfrac{GM_e}{R^2}\mathbf{\hat{R}}.$$
Now one defines $r = R - R_e$ with $\dfr …
1
vote
Which point in the graph does a parachute open?
The parachute can not be opened instantaneously.
The parachute is fully opened at the "vinicity" of the point $C$.
The acceleration due to gravity is constant but there is another force one needs to …