Recent content by lepton5

  1. L

    What is the Proper Method for Calculating Moment of Inertia for a Disk?

    No, I think you can't do that..since in your formula for Idisk still using \lambda as mass distribution in length, while your formula is related to area. you should use \sigma as mass distribution per area and start over.
  2. L

    Boundary condition for magnetic vector potential

    for normal component, using the fact \nabla\cdot A = 0, or write it in integral form, \oint \vec{A}\cdot d\vec{a} = 0, we will get A_{above}^{\perp} = A_{below}^{\perp}. or we can write it in cartesian coordinate, A_{2z} = A_{1z}. for tangential component, Griffith also said that A is...
  3. L

    Simple Harmonic motion (non-calculus)

    sory my bad, mix it up with kinematics. you should you use a (acceleration) for SHM, that is a = \omega ^2 A
  4. L

    (Waves) superposition of 2 pulses along a rope.

    well, actually it comes from \Delta y = y_1 - y_2 = 0. it was based on your information that other wave move oppositely from other one, so the substraction is there.
  5. L

    Simple Harmonic motion (non-calculus)

    time t (period / 4) to reach max velocity from min velocity.
  6. L

    Simple Harmonic motion (non-calculus)

    you can find acceleration just using simple kinematic eqn, that relate Vmax, Vmin, a, t.
  7. L

    Evergy of Simple harmonic motion

    do you know the relation between \omega, k and m ?
  8. L

    Simple Harmonic motion (non-calculus)

    it's more simple if you use energy relation. for maximum velocity, you can equate ME = KE or \frac{1}{2}k A^2 = \frac{1}{2}m v^2. use relation \omega ^2 = \frac{k}{m} and you will get your velocity to about 140m/s
  9. L

    (Waves) superposition of 2 pulses along a rope.

    maybe this way, just equate y1 and y2 to find condition where A = 0 like below, e^{-(x_0 - 2t + 4)^2} = e^{-(x_0 + 2t - 2)^2}, if initially x0 same for both pulse, then you get t = 1.5 s
  10. L

    Is u=qv or u=0.5qv the correct equation for finding potential energy?

    I will try to sharp two eqn above based on common textbook, 1) W = q . [V(a) - V(b)] this eqn tells us for the work done to move a charge from point (a) to point (b). V here means potential difference between points (a) and (b). 2) W = \frac{1}{2}\Sigma^{n}_{i=1} q_i V(r_i) this eqn...
  11. L

    Boundary condition for magnetic vector potential

    Hi, Griffith's fan too here, you see from \mu_o(\vec{K}\times \hat{n}) = \mu_o K(-\hat{y}) automatically x and y component from eqn 1 will dissapear. then, eqn 1 will become eqn 2 as below: -\hat{y}\left[\frac{\partial A_{2z} }{\partial x}-\frac{\partial A_{2x} }{\partial z}-...
  12. L

    Electronics current calculation

    May i help you to solved the problem with another approach (only use V = I R rather than Kirchoof rule). Like this: with R23 = 18.75 you can find voltage here V23 = I1 . R23 = 4.84 V then back to your original circuit diagram. I2 that flow through R2 is I_2 = \frac{V_{23}}{R_2} = about...
  13. L

    EM Theory: Refractive index of water

    Note: this relation n \simeq \sqrt{K_{\epsilon}} (Maxwell Relation) only holds for simple gases (air, Helium, Hydrogen). For water, this relation doesn't work well because K_{\epsilon} and then n are actually frequency-dependent, known as 'dispersion'. You can consult to your Optics book for...
  14. L

    Ratio volume of cylinder inside cone

    use this one, \frac{H - h}{H} = \frac{r}{R}. you are wrong when you use h as denominator at left side, since you have equate it with R (radius of cone) you must also use H (height of cone). can you see : big triangle vs little triangle (from top of cone).
  15. L

    Prove that limit does not exist

    Well, actually you are evaluating the existence of limit by continuity test. maybe if you want to more detail, you can make table for 0^+ (like 1/5, 1/10, 1/100, ...) vs result of limit and for 0^- (like -1/5, -1/10, ...). and check it for left and right - limit (or you can make graph from...
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