Search results

  1. P

    Electron Speed

    This isn't a homework question but if it belongs in another thread please tell me so I can switch it. I was just wondering if there is an "agreed-upon" speed that an electron would travel in say a vacuum? I understand that one can continue adding energy until the electron reaches very nearly...
  2. P

    Friction question!

    Firstly, if it is frictionless then it is not a friction problem lol. What other equation do you think you need to solve this?
  3. P

    Newton and Work

    If you think of it from the point of view of the kid's hands then there is some motion to the kid. He doesn't just catch it with his hands and they (his hands) stay still, rather they move back a certain distance, albeit a relatively small distance. So yes, the ball does do work on the kid...
  4. P

    Aerodynamic force of bird problem

    That sounds right to me.
  5. P

    Kinematics free fall

    displacement = x(final)-x(initial) s = 0-132 When you used 52 m/s (which was your initial velocity) for your motion equation, you get an initial position.
  6. P

    Kinematics free fall

    Did you use a positive acceleration or a negative acceleration? Always remember which way you set up your coordinate system (i.e. down is negative and up is positive.) If you used (-8)m/s for the velocity than we assume down is negative.
  7. P

    Ideal gas law problem in outer space

    1 cubic centimeter = 1.0 × 10-6 cubic meters. When you use a million, you should get: 5.01E-17 Pa, when converted, you end up with 4.8546E-22 atm.
  8. P

    Kinematics free fall

    "Find the displacement of the ball." Since you throw the ball straight up and it comes back down to where you initially threw it from, then I believe the displacement should be zero. It would be like running a lap around the track. Sure you have ran a 1/4 of a mile but your total displacement...
  9. P

    What time does the grinding wheel stop spinning? (constant ang. accel.)

    Homework Statement At t=0, a grinding wheel has omega=24.0rad/s, alpha=30.0rad/s^2 until a circuit breaker trips at t=2s. From then on it turns through 432rad as it coasts to a stop at constant alpha. a) through what total angle did the wheel turn between t=0 and the time it stopped? b) what...
  10. P

    Physics-Bernoulli's Equation

    set bernoulli's equation equal to zero and solve for v. Now since this is an ideal fluid the velocity of fluid flowing through point a, 1.84m, is going to be equal to the velocity of fluid through point b, 0.45m. So you then use the equation for volume flow rate which is dV/dt= A1v1= A2v2, where...
  11. P

    Fourier series

    http://www.intmath.com/ This is an excellent site for what you're looking for...just scroll down to "Higher Calculus" and you should see "Fourier Series."
  12. P

    To the man part 2

    "No, we will not just skip checking posts" You misunderstood me here, I was referring to the smug comments that could be done without. You said you saw the thread and just decided to not enter it. Everyone who feels there time will be wasted shouldn't enter it, but you must remember that there...
  13. P

    To the man part 2

    "I think that there is a "Banned Topics" list someplace here, with explanations for why they are banned as non-useful topics. Maybe we need to work more at expanding that list as a FAQ for newbie posters..." perhaps..or create a section where hypotheticals can be freely asked...
  14. P

    To the man part 2

    All I'm trying to get at is that it should be fine to talk about almost anything as long as it is in the correct thread of course. You said:"Boy, that's an unproductive thread. Not a possibility from the get-go, so why waste time on it instead of on something real and potentially productive."...
  15. P

    To the man part 2

    What you call "uptight" is what 200,000 people call "quality control". Quality control is one thing but what upset me was a post I read about what it would be like to be light, hypothetically of course. The main antagonist, i.e. one of the moderators, couldn't seem to open up his mind and...
  16. P

    To the man part 2

    yes dave that's the one
  17. P

    To the man part 2

    why lock the thread? are you guys afraid to hear peoples' opinions on how you choose to run things? I think you should hear what some of us have to say...after all this is the feedback section...geez Guidelines on Language and Attitude: Foul or hostile language will not be tolerated on Physics...
  18. P

    To the man

    to the people who operate this website... i've browsed through so many posts that are simply hypothetical or simple thoughts intended to spark others' imaginations. And within these posts I see so many PF Contributors and whatnot getting their panties in wad over questions they feel aren't...
  19. P

    Integral of sin(2x)dx

    ah so that's where I went wrong...I tried u substitution but I used u=sin2x instead of u=2x. thanks mark44.
  20. P

    Integral of sin(2x)dx

    Homework Statement \int sin(2x)dx Homework Equations I know the integral of sin(x)dx = -cos(x) + C The Attempt at a Solution What I did was to say that the integral is -cos(2x) +C, which isn't the correct answer...I should have gotten -1/2(cos(2x)) +C. I can see that this is the correct...
  21. P

    Applying variational principles to that metric describes a black hole!

    in M. Alcubierre's equation the "s" in the superscript of "v and r" are supposed to be subscripts, I just couldn't get them to work. btw
  22. P

    Applying variational principles to that metric describes a black hole!

    ds^{2} = -c^{2}(1 - \frac{2Gm}{c^{2}r})dt^{2} + (1 - \frac{2Gm}{c^{2}r})^{-1} dr^{2} + r^{2}d\Omega^{2} This equation was posted on a different website and the O.P said:"Applying variational principles to that metric describes a black hole!" I was wondering if anyone could explain it a...
  23. P

    Switch in a circuit

    I believe it has something to do with how a capacitor only stores electrons. A capacitor works via the use of two plates; one hooked up to the positive terminal of say a battery and the other to the negative end. The electrons become stored in the plate attached to the negative terminal of the...
  24. P

    Sunset-Sunrise reversal?

    I understand how directions work. Of course we wouldn't say that. I'm ultimately getting at how east and west (and even north and south) are just constructs of the human mind. In particular, east and west were created to compensate for the way in which the sun seems to rise and set. What I want...
  25. P

    Sunset-Sunrise reversal?

    Ok I'll give into it not being time travel :approve:, but what about the directions? Is it safe to assume that east and west are just illusions of Earth's rotation?
  26. P

    Sunset-Sunrise reversal?

    For someone flying in say a SR-71 which holds an absolute speed record of 1,905.81 knots (2,193.2 mph; 3,529.6 km/h); if they flew long enough in the direction opposite of the Earth's rotation from somewhere like NC(35° 38' 27" N / 79° 50' 35" W) would they be traveling backwards in time? Or...
  27. P

    Sunset-Sunrise reversal?

    Sunset-Sunrise reversal? If you got in your airplane an hour after the sun has already set, say in North Carolina, and traveled west towards California, would you end up seeing the sun rise in the west and eventually (if you could travel fast enough and head towards China) see the sun set in...
  28. P

    Emission Spectrum

    I was just wondering if anyone knew of anywhere on the internet that had a list of all known emission spectrums of the elements. Thanks!
  29. P

    I want to know that light has mass or not.

    Light consists of packets of energy called photons which are massless particles, so the short answer would be no. However, it really depends on what kind of mass we're talking about. According to E=mc^2 mass and energy are the same thing, and since light has energy, it should have a mass. But...
  30. P

    Energy Conservation - Electric Potential Energy

    "Express your answer to two significant figures and include the appropriate units." It should be 7.7x10^-9 C
  31. P

    Potential difference in a circuit

    The voltage of the battery and the current times the resistance are equal. Voltage as pressure in a water tank is the example that comes to mind. Think of it as the pressure in the water tank doesn't go anywhere (it is the h2o that moves because of the pressure) but it just kind of dissipates in...
  32. P

    What is the speed of the crate when it reaches the bottom?

    Homework Statement A 20.0-kg crate slides down an inclined plane that is 3.00-m high and 20.0-m long. If friction is negligible, what is the speed of the crate when it reaches the bottom of the plane? Homework Equations W= F*D K= 1/2 m*(v^2) The Attempt at a Solution They don't...
  33. P

    Schools Grad School Preparation

    But considering that I would like to pursue theoretical physics, would it make more sense to have a more solid foundation in mathematics?
  34. P

    Double Slit Experiment inquiry

    Say if we had the gun at a distance A from the slit, and the slit a distance B from the plate and we ran the experiment to obtain our first pattern. We then proceed to run the experiment again with both A and B increased by a particular factor. I guess my real question then, is whether or not...
  35. P

    Double Slit Experiment inquiry

    Does the distance from the photon/electron gun to the slit matter at all? Or even the distance from the slit to the photographic plate?
  36. P

    Schools Grad School Preparation

    Would earning a B.S in Mathematics and a B.A in Physics look better for graduate school consideration, or a B.S in Physics and a B.A in Mathematics?
  37. P

    Schools Graduate schools

    Would earning a B.S in Mathematics and a B.A in Physics look better for graduate school consideration, or a B.S in Physics and a B.A in Mathematics?
Top