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Homework Help: Question about centripetal acceleration

  1. Oct 16, 2007 #1
    1. The problem statement, all variables and given/known data
    A centripetal-acceleration addict rides in uniform circular motion with period T = 6.12 s and radius r = 3.00 m. At one instant his acceleration is a = (1.00 m/s2) i + (-3.00 m/s2) j. At that instant, what are the following values? v.a and r x a

    2. Relevant equations

    T = (2pi r) / v

    3. The attempt at a solution
    i am not sure what to do here. i can plug T and r into one of the uniform circular motion and get a velocity value but it is not in vector notation so i don't know how i would find the dot product
  2. jcsd
  3. Oct 17, 2007 #2
    You have the right idea for finding the angular velocity. You have your equation and everything, simply move the variables around until you have an equation that will get you velocity.

    [tex]v = \frac {2\pi r}{T}[/tex]
    [tex]v = \frac {18.85}{6.12}[/tex]
    v = 3.08 radians per second or rad/s

    Unfortunately, I am not sure what you are asking for on the second part though, so I am not sure how to help you on that part. Sorry.
  4. Oct 17, 2007 #3
    the actual question asks for v dot a and r cross a. for v dot a i think you can use abcos theta but i don't know how to find the angle.
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