# Recent content by jamdr

1. ### Superposition of electric fields from uniform charge density

Can I replace Q with this: Q=\sigma 4\pi R^{2} That would mean the electric field from the spherical shell is: E_{shell}= \frac{\sigma}{\epsilon_{0} } Although I'm still not sure about the direction part of if anything else I've done so far is correct.
2. ### Superposition of electric fields from uniform charge density

I got the equation for the spherical shell from my textbook, which uses it as an example. It says this about it: Electric field due to a uniformly charged spherical shell. Outside the shell, the field lines have spherical symmetry: they diverge from the origin. The field line pattern is the...
3. ### Superposition of electric fields from uniform charge density

Homework Statement Ok, here's the problem. It deals with the superposition of electric fields from uniformly charged shapes: A uniformly charged infinite plane is located at z = 0, with a surface density of charge σ. A uniformly charged spherical shell with the same surface density is located...
4. ### Using Fourier analysis to find frequency-amplitude spectrum?

Thanks for the help Dr. Transport. But in the end I ended up using this formula: f_n=\frac{1}{T}\int_0^T v(t) e^{-j n \omega t} dt where n is some arbitrary number of coefficients. Also, n is the index of f (an array). Then I plotted \overrightarrow{\left|f\right|}_n versus \frac{n}{T}...
5. ### Using Fourier analysis to find frequency-amplitude spectrum?

Wait, what is a?
6. ### Using Fourier analysis to find frequency-amplitude spectrum?

It's a math question I suppose. I need to know the steps to find a fourier transformation. I know that MATLAB and other computer programs can solve this type of problem, but I want to understand the math behind it.
7. ### Using Fourier analysis to find frequency-amplitude spectrum?

The signal is from a voltage supply. I see lots of pages on the internet about this, such as this one, which shows what the magnitude spectrum looks like for a square wave with an arbitrary number of co-efficients. But how would I actually create that graph myself?
8. ### Pressure on a submarine window problem

I have this fluids problem I've been working on for a while, but I can't seem to get the correct answer. The problem is: A circular window with radius 25 cm in a submarine can withstand a maximum force of 1.23E6 N. If the interior of the submarine is maintained at a pressure of 1 atm...
9. ### Help with fluids

I have these two fluids problems and I can't get either one (they are related). Can anyone point me in the right direction? 1. A 3.05 kg piece of wood (SG = 0.500)) floats on water. What minimum mass of copper, hung from it by a string, will cause it to sink? 2. A 3.25 kg piece of wood (SG...
10. ### Conservation of momentum of a boat

I know I'm probably a few months late and I doubt you need the answer anymore, but I'll post this in case someone else comes across a similar problem. You were going in the wrong direction with your solution. This is not a conservation of momentum problem; it is a center a mass problem...
11. ### A simple pulley problem

Correction Thanks, Doc. The correct answer is indeed 214 N. I meant that the method Halls used to solve it was correct, although I went through the calculations and plugged in the numbers myself. It is easier to use Newton's 2nd Law. I had tried this the first time, but arrived at the wrong...
12. ### A simple pulley problem

That works Thanks for the reply. I think I follow your reasoning, although you did it differently than I did (I was trying to analyze the system only in terms of Newton's second law). The answer is correct, though. :smile:
13. ### A simple pulley problem

I'm working on this rather simple pulley problem, and can't quite figure it out. It doesn't even involve acceleration. Could anyone help me out? Thanks. Here's the problem: A crate is pulled up using frictionless pulleys in the manner shown in the figure. The angle is 45 degrees. The masses...