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Homework Help: Motion in Polar Coordinates problem

  1. Apr 19, 2009 #1
    Been looking over past exam questions and came across this one. Its in polar coordinates:

    A particle P describes the curve r=be^[Zcot(a)].

    Show that the velocity and acceleration vectors have angles a and 2a with OP (O is the origin).

    Z is actually theta, the angle the position vector makes with the x axis. Its derivative to time is w, a constant here. B and a are constants.

    I'm stumped!!!!

    I work out v as: bcot(a)we^(Zcot(a)).[e_1] + bwe^('').[e_2]

    Even with them worked out I am stumped as to show that^^^^

    Any pointers???

    Cheers guys!!!
  2. jcsd
  3. Apr 20, 2009 #2


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    Homework Helper

    Hi Master J,

    I would suggest first simplifying this expression for v, using the expression for r given in the problem. Then, since they ask for the angle between two vectors, that suggests using the dot product (since one definition of the dot product explicitly includes the angle between the vectors). Do you get the answer?
  4. Apr 20, 2009 #3
    SOlved! Thanks for the help.
  5. Apr 20, 2009 #4


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    Homework Helper

    Sure, glad to help!
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