Plane Trigonometry

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A compact disk is 12 cm in diameter & rotates at 100 rpm when being played. The hole in the center is 1.5 cm in diameter. Find the speed in cm/min of a point on the disk & the speed of a point on the inner edge.

  • Plane Trigonometry -

    A revolution is 2 pi radians
    So it goes w = 200 pi radians/minute

    tangential speed = w r = r * 200 pi

    at outside
    v = 6*200 pi cm/min

    at inside
    v = 0.75 * 200 pi cm/min

  • Plane Trigonometry -

    Hi!Thanks for the answer. Might I ask what w represents?

  • Plane Trigonometry -

    w is Greek omega (I do not have Greek letters on my keyboard), the angular speed in radians per unit time.

  • Plane Trigonometry -

    If you have not studied that use:

    Circumference at any radius = 2 pi r

    Number of circumferences per minute = 100

    so at any radius r

    speed = 100 * 2 pi r = 200 pi r

  • Plane Trigonometry -

    Thanks again!:)

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