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Polar Coordinates of a car

  1. Sep 2, 2007 #1
    1. The problem statement, all variables and given/known data

    A car P travles along a straight road with a constant speed v = 65mi/hr. At the instant when the angle theta = 60 degrees, determine the values of r (with dot above) in ft/sec and theta (with dot above) in deg/sec. (r = 100ft)

    The picture has a car on highway and radius pointing diagonally from the origin which is on the field in "/" like this.

    2. Relevant equations

    Vr = r (with dot above)
    Vtheta = r*theta(with dot above)
    v = sqrt(((Vr)^2)+((Vtheta)^2))

    3. The attempt at a solution

    Vr = v cos theta and found Vr without a problem.
    I tried to plug in v = 65mi/hr (converted to ft/sec) into 3rd eqn with Vr in order to find Vtheta. After that I substitude it into 2nd eqn since I know the radius. I got the theta value and converted to deg/sec from rad/sec but I am not getting answer.

    What mistake have I made? :(

    Thank you.
  2. jcsd
  3. Sep 2, 2007 #2


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    Homework Helper

    What is the position of the car relative to the origin, and what direction is it moving in?
  4. Sep 2, 2007 #3
    wow, i just made the stupidest mistake ever...
    i JUST realized that radius is NOT 100 hahaha
    sorry about that! and thank you!
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