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Homework Help: Rotational motion

  1. Jun 29, 2010 #1
    1. The problem statement, all variables and given/known data
    The diameters of the main rotor and tail rotor of a single-engine helicopter are 7.63 m and 0.99 m, respectively. The respective rotational speeds are 459 rev/min and 4132 rev/min. Calculate the speeds of the tips of both rotors.

    2. Relevant equations

    3. The attempt at a solution
    V=(3.815m)(7.65 rev/s)
    V=29.18 m/s

    V=(.495m)(68.89 rev/s)
    V=34.10 m/s
  2. jcsd
  3. Jun 29, 2010 #2


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    Homework Helper
    Gold Member

    Hello mandy9008,

    Not quite. Your relevant equation is good, but your application of it is missing a little something. Here are a few clues:

    What is the circumference of a circle in relationship to its radius?

    Following the same idea, if something travels around a circle once in a given amount of time, what total distance does it traverse? And at what speed?

    Which is really the same question phrased differently, what is the relationship between the angular frequency ω (in radians/sec), and the rotational frequency f (in rotations/sec)?
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