Search results

  1. T

    Oxidation of iron

    That's what I thought, but it is much easier to oxidize iron than either water or hydroxide according to the values I found... Why do I not get any iron hydroxide?
  2. T

    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...
  3. T

    Angular momentum at a distance

    Thanks. That was the same as mine but much neater.
  4. T

    Angular momentum at a distance

    Never mind, I managed to prove it. Thanks!
  5. T

    Angular momentum at a distance

    Thanks a ton! This is exactly what I was looking for. Do you know of a proof of this?
  6. T

    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...
  7. T

    Size of planet with 1/50 gravity of earth

    The universal law of gravitation is: F_g = \frac{mMG}{r^2} Where G = 6.674*10^{-11} \frac{m^3}{kg*s^2} The average mass density of the earth is 5.515 g/cm^3 (According to Wikipedia), so the acceleration due to gravity based on a planet with Earth's density and radius r is a =...
  8. T

    Average velocity question

    You got speed right, speed is distance over time. Velocity is actually displacement over time.
  9. T

    RLC circuit voltages

    You need to use Faraday's law to properly understand inductors. What is often misunderstood about inductors is that there is no voltage drop across an ideal inductor, it imposes an EMF in the opposite direction. Kirchhoff's law does not hold for inductors. What does hold is: \oint_C...
  10. T

    Impact Physics

    You could approximate what would happen to an accurate degree. You would need to know the mass distribution of the horseshoe and the friction coefficients between the shoe and the stake, but a computer simulation would be possible.
  11. T

    Spring causing a mass to jump

    Ok, I see. Easy mistake: x = \frac{4mg}{k} It seems everything else I did was unnecessary, I don't need to deal with the potential energy. So evaluating the integral: \int_{\frac{-4mg}{k}}^{d} (-kx - mg) dx = 0 Yields: d =\frac{2mg}{k} M \lt 2m This makes sense, Thanks!
  12. T

    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)
  13. T

    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...
  14. T

    Faraday's Law Lecture Error?

    You're right: The closed loop integral of E dot dl is minus the change in magnetic flux through the open surface attached to the loop.
  15. T

    Transistor not gate function

    Thanks for the link, that was a good description, the only part I don't understand is: I don't see why R3 doesn't increase the output resistance
  16. T

    Transistor not gate function

    The 0 volt arrows just indicate a zero volt difference, so the diode doesn't activate. Because Q3 and D2 don't seem to significantly change the output voltage, I think you're probably right, they're probably protecting the circuit from back feed current. They were confusing because they...
  17. T

    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...
  18. T

    Evaluating a line integral

    The first and last terms of your integral should be easy to evaluate, the possibly tricky one is the middle term. The trick is to use the half-angle identity: \cos^2 \theta = \frac{1 + \cos 2\theta}{2}
  19. T

    Calculating line integrals

    This problem illustrates how nice it can be to notice that the vector field in this problem is a vector field. If you notice that the potential function is f(x,y) = \sin(xy^2) + c then it is easy to find an answer. The answer found this way would agree with @grey_earl's indefinite integral.
  20. T

    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...
  21. T

    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)...
  22. T

    How does a rigid block on its edge move?

    I calculated the moment of inertia to be 5, but I'm not sure how to use conservation of energy because I don't know how to calculate gravitational potential energy on this object.
  23. T

    How does a rigid block on its edge move?

    Maybe I haven't reached the appropriate topic yet, but what I want to see is how the object rotates about the stationary point due to gravity. By infinite friction I mean the bottom point is stationary, does not slide.
  24. T

    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):" [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...