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Poiseuille's law- Radius vs Flow speed

Discussion in 'MCAT Study Question Q&A' started by IlyaR, Jan 13, 2014.

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  1. IlyaR

    IlyaR 2+ Year Member

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    Jun 5, 2013
    I was going over the wiki premed cards and couldn't decide whether there was an error or if I'm just not understanding something

    [​IMG]

    Should the answer be a exponential, with a curve towards the x axis?

    According to the equation,

    AV=dP(pi)r^4/constant

    V(pi)r^2=dp(pi)r^4/constant

    V=dp(r^2)/constant
    So...as TBR says...the graph curves towards the axis which displays greater change.

    Am I wrong here?
     
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  3. Lifeman

    Lifeman 7+ Year Member

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    Jul 28, 2008
    just graph y=x^4
     
  4. Odi

    Odi

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    Jan 7, 2014
    Doubling the radius causes an increase in flow rate of 16X

    If everything is held constant than Q=r^4

    Doubling the radius Q=(2r)^4=16r^4

    The flow rate increases 16x as the radius is increased by a factor of 2x. Flow rate is changing more quickly so D is most reflective of this.

    What's the answer on the card?
     
  5. IlyaR

    IlyaR 2+ Year Member

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    Card says d. But what I don't get is why it's bending towards the y axis. R isn't increasing more than v
     
    Last edited: Jan 13, 2014
  6. Odi

    Odi

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    92
    Jan 7, 2014
    I see what you're saying. If the axes labels are as is than yeah the graph should resemble x=y^4 and curve to the x axis... not y=x^4 as is.

    Looks like they labelled their y and x axis wrong.
     
    IlyaR likes this.
  7. IlyaR

    IlyaR 2+ Year Member

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    Jun 5, 2013
    Cool. Just needed someone to confirm my suspicions lol.
     

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