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Homework Help: Electron Problem

  1. Jan 10, 2005 #1
    An electron moves in a plane so that at time t its coordinates are

    x = a( e^t + e^-t) and y = b(e^t - e^-t) . How fast is its distance from the origin changing?

    My solution:

    Let Y be the distance from the origin and the point

    Then using distance formula I get

    Y = [[a( e^t + e^-t) ^2] + [[b(e^t - e^-t)^2]

    Do I just find derivative of this?
  2. jcsd
  3. Jan 10, 2005 #2
    y is not the distance between origin and point, r=sqrt(x^2+y^2), do the derivative of r and you will see the answer
  4. Jan 10, 2005 #3
    isnt that what i have??
  5. Jan 10, 2005 #4
    one more things, sinhx=(e^x-e^-x)/2 coshx=(e^x+e^-x)/2, hope tis will make the calculation simpler, IF you have not learned the derivative of these yet, just forget it....
  6. Jan 10, 2005 #5


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    Science Advisor
    Homework Helper

    Nope,u miss the square root...

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