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Homework Help: Finding the speed of car A and car B

  1. Feb 10, 2010 #1
    1. The problem statement, all variables and given/known data

    At the instant shown, race car A is passing race car B with a relative velocity of 1ft/s. Knowing that the speed of both cars are constant and that the relative acceleration of car A with respect to Car B is 0.9ft/s^2 directed toward the center of curvature, determine the speeds of cars A and B.

    The diagram is located here: Problem 134


    Thank you!

    2. Relevant equations

    3. The attempt at a solution

    With the relative acceleration being what it is in the j direction, I plugged in 0.9 = vb^2/p - va^2/p and plugged in a 3+Va for vb. That doesnt work. What should I do here?

  2. jcsd
  3. Feb 10, 2010 #2


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    Homework Helper

    Acceleration of the car in a circular motion is
    a = v^2/r. Or
    a*r = V^2.
    So for larger radius acceleration is smaller. For car A
    a*r(a) = V^2.........(1)
    For car B
    (a - 0.9)r(b) =(V+3)^2....(2)
    Solve the two equations.
  4. Feb 10, 2010 #3
    doing that I get an unsolvable quadratic....
  5. Feb 10, 2010 #4


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    Homework Helper

    The two cars are moving together with constant velocity. So they must have the same angular velocity.
    The acceleration a = ω^2*r.
    So (a + 0.9) = ω^2*300
    and a = ω^2*290. Now solve for a.
    Then use a = V^2/r to find velocities of the cars.
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