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  • Users: jix
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  1. J

    Find frequency and period of oscillation

    Could you show how you got that?
  2. J

    Electric Field

    If you move up an electric field, the potential increases. Suppose that for points A and B, the potential at B is higher. Then moving from A to B, the distance is, say, positive, and so the potential difference is also positive. But then the eletric field is directed from B to A, and so is...
  3. J

    Angular Magnification for mirrors and lens

    How about this: parallel light rays, makng a small angle α with the optical axis of a spherical concave mirror, where will the rays focus? First of all, do they focus on the same plane (perpendicular to the optical axis) as the focal point, and secondly, how far from the axis? That's the...
  4. J

    Angular Magnification for mirrors and lens

    Homework Statement I'm looking for someone to clarify a strange result regarding angular magnification. For both mirrors and lens. Homework Equations m(angular) = θ'/θ M(lateral) = h'/h = - d'/d θ ≈ h/d (for small angles) The Attempt at a Solution Using the angle equation, I get a...
  5. J

    Hurricane wind blowing across a flat roof

    That's not the right equation. Rather, it's not the entire equation. First of all, the numbers you used don't even turn out to have the right units. As in, d = 93.6 m^2 doesn't have the right units for d. And think about it, the speed is given for a reason. Get the full equation, and plug...
  6. J

    What is the magnitude of the magnetic field?

    theta is the angle made between the normal to the coil to the magnetic field. Think about it, if the coil is parallel to the magnetic field (theta = 0), the torque is maximum (the forces on the wires are directly opposite), as opposed to if you used sin 0 = 0, that is torque = 0. So you have to...
  7. J

    Second year uni, e&m, dialectrics question?

    Rings are key. Split the disk into infinitesimal rings. I assume you have a decent handle on calculus, so first derive the electric field at distance b from a ring of radius r and thickness dr. Like, take infinitesimal segments (on an infinitesimal ring!) and calculate the fiield, integrate...
  8. J

    Physics impulse

    Yay seatbelts! 9 m = 3+ stories. Add to that the fact that your centre of mass will travel further than 0.3 m over the deceleration, the deceleration is less than 33 G's. Since a 3 storey fall is likely to break something or another, 33 G's is too much to get through without significant injury.
  9. J

    Physics impulse

    Well, even so, it would be for hitting a wall, which would really hurt. Compared to hitting another car, the collision time is a lot shorter.
  10. J

    Electron velocity when beam is restored by a magnetic field.

    You don't need the circular motion equation (if that's what it is). The forces of the magnetic and electric fields are simply opposite each other, and equating will give you the answer.
  11. J

    Where has the energy of the closed photon packet gone?

    Additionally, there is a gravitational shift. The photon, with an effective mass of hf/c^2, has a negative gravitational potenial, which is gained as photon energy as the photon moves away from the gravitational field. Since the gravitational potential increases (to zero), the total energy of...
  12. J

    Simple pendulums

    Redo the calculation, perhaps, and divide period by 4, since reaching the bottom takes one-quarter of the period.
  13. J

    Electrostatic Problems

    1) There shouldn't be a force on the insulator. The reason for polarization is because the repulsive force on the like charges, when further away from the comb, is less than the attractive force on the unlike charges closer to the comb. Therefore the insulator becomes polarized. But if the...
  14. J

    Impulse, help!

    First of all, there's no time, so impulse cannot be found. Also, you cannot analyze a collision of any sort withou knowledge of what kind of collision it is. Therefore the total momentum of the system is a useless value, because you don't know if the collision is elastic, inelastic, or...
  15. J

    Physics impulse

    Notice that the velocity over the 1 foot is not constant, so the time interval you calculated is incorrect. In fact, you should use the v^2 = v0^2 - 2ax formula to calculate the acceleration (assumed to be constant here), and then the force. Hope that gives you the right answer.