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Homework Help: Motion in a circle of helicopter rotor

  1. Jul 12, 2007 #1
    1. The problem statement, all variables and given/known data
    A model of a helicopter rotor has four blades, each 3.20m in length from the central shaft to the blade tip. The model is rotated in a wind tunnel at 600rev/min. a.) What is the linear speed of the blade in m/s?
    b.) What is the radial acceleration of the blade expressed as a multiple of the acceleration due to gravity g?

    2. Relevant equations
    [tex] a_{rad} = \frac{V^2}{R}[/tex]
    [tex] a_{rad} = \frac{4{\pi}^2R}{T^2}[/tex]

    3. The attempt at a solution
    a.) convert: 600rev / min ( 1 min / 60secs) = 10 rev / s
    Multiplied 3.20m by 10 rev / s = 32.0m/s?

    b.) [tex] a_{rad} = \frac{V^2}{R}[/tex]
    a_{rad} = (32.0m/s)^2 / (3.20m) = 320m/s^2

    i dont understand the radial acceleration of blade expressed as a multiple of g....
    is my answers correct?
  2. jcsd
  3. Jul 12, 2007 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Careful. To convert between linear and angular speed, use [itex]v = \omega r[/itex], where [itex]\omega[/itex] is in radians/sec, not rev/s.

    Alternatively, realize that 1 revolution covers 1 circumference, which equals [itex]2 \pi r[/itex].

    Redo this with the correct speed.

    Since g = 9.8 m/s^2, just divide your answer by that value to get an answer as a multiple of g.
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