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Thread: Circular Disk

  1. #1
    Super Member harpazo's Avatar
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    Circular Disk

    How many revolutions will a circular disk with a diameter of 4 feet have to complete after it has rolled 20 feet?

    Question:

    How is this done without trigonometry? Every time I see the word REVOLUTIONS, I quickly think trigonometry.
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  2. #2
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    Re: Circular Disk

    No trig needed here.
    What measurement of the circle do you need to calculate first?
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  3. #3
    Super Member harpazo's Avatar
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    Re: Circular Disk

    Quote Originally Posted by Debsta View Post
    No trig needed here.
    What measurement of the circle do you need to calculate first?
    I must calculate the circumference first, right? If so, the formula C = pi•d comes in handy. I will check your reply in the afternoon today.
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  4. #4
    Super Member harpazo's Avatar
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    Re: Circular Disk

    The distance rolled in a single revolution is the circumference of the disk. This is pi(d), where d is the diameter. So, in this case that is 4•pi.

    To get the number of revolutions can I divide 20 by 4pi?

    Let R = number of revolutions

    Let C = circumference

    R = 20/C

    R = 20/4•pi

    R = 5/pi

    Is this right?
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