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  • Users: don23
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  1. D

    Is this a trick question?

    A horizontal beam of light is reflected from a plane mirror that revolves about a vertical axis at a rate of 30 rev/min. The reflected beam sweeps across a screen that, at the point nearest the mirror, is 20 m away. With what speed does the spot of light move across the screen at the point...
  2. D

    2 tough questions

    I need help with these two questions: 1. A particle of mass 'm' and charge '-q' moves in a circular radius 'R' about a fixed charge 'Q.' The angular frequency for the orbit is given by w0^2=q*Q/(4*pi*e0*m*R^3). A uniform magnetic field of magnitude B is in the direction perpendicular to the...
  3. D

    Calc 3 easy question

    calc 3 easy question! I am trying to find the partial derivative of the following function with respect to y. I know how to find it without using the definition...but i want to know how to do it both ways. any help?? g(x,y)=x^2*e^-y I got: lim as h approaches h...
  4. D

    Potentials of charge distribution

    The question says that charges are distributed with uniform charge lambda along a semicircle of radius R, centered at the origin of a coordinate system. What is the potential at the origin? I am not sure how to approach this one. Can anyone help me set this up and solve it? Thanks!
  5. D

    Quick calc limit question

    thank you thank you:) it's been a while...i forgot about l'hopital's rule. thanks again
  6. D

    Quick calc limit question

    can someone help me out with a simple calc question? we are asked to find the limit of a function as t approaches zero. the function is: (sint/2t)i + (e^2t)j + (t^2/e^t)k why is the answer not just j? the answer given is 1/2i + j, but I have no idea how that first term came about...
  7. D

    Some quick calc questions

    ok, first what is e^t times e^-t? and can anyone help with this one: the integral from 0 to pi of (sinti+costj+tk)? is it -costi + sintj +(t^2/2)k? thank you!
  8. D

    Electric field

    thank you thanks again. in this case wouldn't the distance from the origin be (sq rt of (a^2+a^2))? In the original problem all the charges are at (a,a),(-a,a),(-a,-a) and (a,-a).
  9. D

    Electric field

    thanks Thank you for the reply. would i be correct is saying that E= (+q*k/a^2+a^2)+(+q*k/a^2+a^2)+(-q*k/a^2+a^2)+(-q*k/a^2+a^2)= 0 ??
  10. D

    Electric field

    Can someone help with this? I want to say the answer is zero but I don't know how to explain it. Calculate the electric field at the origin due to the following distribution of charges: +q at (x,y)=(a,a), +q at (-a,a), -q at (-a,-a) and -q at (a,-a).