Tagged Questions
-3
votes
2answers
105 views
Why is $r'/r^2 = -1/r$? [closed]
If $r=r(t)$, why is $\frac{r'(t)}{(r(t))^2}$ = $\frac{1}{r(t)}$ where $'$ denotes the derivative? I saw it in a lecture.
Can you please explain?
0
votes
1answer
120 views
Control system with equation C = A*x + B*dx/dt
This question came up in a computer science / robotics exam and I still don't know the solution for it. I figured out that it's classical mechanics related, so I thought this might be the best place ...
0
votes
1answer
134 views
Looking for a way to simplify a physics formula [closed]
I have the following physics formula:
$$d = \frac{1}{2} at^2$$
where d is equal to half (at) squared
where:
d is distance
a is acceleration
t is time
I need to simplify this to get the ...
2
votes
2answers
520 views
Calculating uncertainty in the final result (combining uncertainties)
I'm struggling to determine the uncertainty in $F$ so it would match the textbook answer.
The problem statement is: A force F is obtained using the equation: $F = \frac{mv^2}{2\pi(x_2 - x_1)}$.
The ...
-1
votes
1answer
253 views
Functional Derivative of Convolution
How to carry out the following functional derivative?
$$\frac{\delta F}{\delta n(r)}$$ where $$F=\int dr n(r) \int C(|r-r'|) n(r') dr'$$
is it simply:
$$2 \int dr' C(|r-r'|) ...
3
votes
0answers
451 views
How do I derive the critical temperature for bose condensation in two dimensions?
In class we derived the 3D case, but there's a step I don't understand:
$$ N = g \cdot {V \over (2 \pi \hbar)^3} \cdot \int\limits_{0}^{\infty}{1 \over{e^{\left( E_p \over{K_B T}\right)}-1}} d^3 p = ...
