# Search results

1. ### Oxidation of iron

I've got a question that is bugging me If I have a concentrated sodium hydroxide solution and electrolyze it with iron electrodes, some of the possible reactions at the positive electrode are 2H2O -> O2 + 4H++4e-. Eo = -1.23 V 4OH- -> O2 + 2H2O + 4e-. Eo = -0.40 V Fe -> Fe2+ + 2e-. Eo = 0.44...
2. ### Angular momentum at a distance

Say I have a situation like the image. I have a potentially complex object with moment of inertia I about its center of mass, mass M, velocity v and position r with respect to P. It is rotating with angular velocity ω about its center of mass What is the angular momentum about point P? I...
3. ### Antenna length

I have been looking into how antennas work, and I have found that antennas of half wave-length are apparently optimal, but I don't understand why. If anybody could explain why this is, I would appreciate it. Thanks! (I do have an understanding of electromagnetic waves)
4. ### Spring causing a mass to jump

This is not a homework/coursework problem, but I came across it and wanted to check my answer. Homework Statement As in the diagram, there are two blocks of mass M and m. The mass m is suspended above M by a spring of spring constant k. Initially, the block m is pushed down with a force...
5. ### Transistor not gate function

Transistor "not gate" function I've been trying to understand the following circuit: I'm new to circuitry and electrical engineering, so I've had some trouble understanding the function of transistor Q3 and diode D2, I believe the circuit should function without them. If anybody could...
6. ### Safety of small angle approximations

Today I was doing a problem (physics) and ended up with the a differential equation dT = -µ T sin(dθ) (Where µ is constant) I wasn't sure what to do with the sin(dθ), so I used the small angle approximation of sin(dθ) = dθ. I would think this would be a perfect approximation because dθ is...
7. ### Pulling a yo-yo on a table.

Hello pf! I'm self-studying physics on MIT OCW, and I'm confused about one of the challenge problems. (attached) I'm looking at problem #2, and I thought I had it understood, but when I looked at the solution the first thing that is stated is that τ = Rf - bF (f = the force of friction)...
8. ### How does a rigid block on its edge move?

I am self studying physics, and a problem that I have not been able to figure out has been bothering me. Look at the image (also attached): http://imgur.com/xHP2S" [Broken] Let's say that the side length is 1 m. and the mass is 10kg. The object has no initial velocity and assume there is...