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    I cannot for the life of me figure out why the answer to the following question is 2π^2mf^2D...

    "A disc of diameter D is turning at a steady angular speed at frequency f about an axis through its centre.

    What is the centripetal force on a small object O of mass m on the perimeter of the disc?"

    Why would the answer not just be m2πf^2D/2?

    F=mω^2r,
    ω= 2πf
    so F=m2πf^2D/2?

    Someone please help.
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    Hi Swifty 21,

    When you substitute ω= 2πf into your equation for F you get

    F=mω^2r = m(2πf)^2r = m(4π^2f^2)r = 4π^2mf^2r = 4π^2mf^2(D/2) = 2π^2mf^2D

    Hope this helps.
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    (Original post by swifty21)
    I cannot for the life of me figure out why the answer to the following question is 2π^2mf^2D...

    "A disc of diameter D is turning at a steady angular speed at frequency f about an axis through its centre.

    What is the centripetal force on a small object O of mass m on the perimeter of the disc?"

    Why would the answer not just be m2πf^2D/2?

    F=mω^2r,
    ω= 2πf
    so F=m2πf^2D/2?

    Someone please help.
    Basically, you've forgotten to square the 2π as well as square the f

    F = (mv^2)/r
    = m(ω^2)r
    = m(ω^2)D/2
    = m((2πf)^2)D/2
    = 4m(π^2)(f^2)D/2
    = 2m(π^2)(f^2)D
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    (Original post by Teenie2)
    Hi Swifty 21,

    When you substitute ω= 2πf into your equation for F you get

    F=mω^2r = m(2πf)^2r = m(4π^2f^2)r = 4π^2mf^2r = 4π^2mf^2(D/2) = 2π^2mf^2D

    Hope this helps.
    Yeah thank you very much, I understand now!
 
 
 
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