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Math Help - [SOLVED] Need help with related rates problem.

  1. #1
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    [SOLVED] Need help with related rates problem.

    The Problem:
    Grain is pouring out of a hole in the bottom of a large inverted cone with a vertical angle of 90 degrees at the rate of 7 m^3/min. Find the rate, in cm/s, at which the depth of grain in the cone is changing when the depth is 1.2m.

    I don't understand how I find the radius.
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  2. #2
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    Quote Originally Posted by swatpup32 View Post
    The Problem:
    Grain is pouring out of a hole in the bottom of a large inverted cone with a vertical angle of 90 degrees at the rate of 7 m^3/min. Find the rate, in cm/s, at which the depth of grain in the cone is changing when the depth is 1.2m.

    I don't understand how I find the radius.
    were you given the dimensions of the cone?
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  3. #3
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    No I was not.
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  4. #4
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    I believe you were probably given that the vertex angle of the cone is 90 degrees ...

    sketch a picture and you will see that r = h for any amount of grain in the cone.

    V = \frac{\pi}{3}h^3

    can you proceed from here?
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  5. #5
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    Well I'm not a hundred percent sure what the vertex angle means?
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  6. #6
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    Quote Originally Posted by swatpup32 View Post
    Well I'm not a hundred percent sure what the vertex angle means?
    the vertex angle is the angle at the pointy end of the cone
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  7. #7
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    Okay but I still don't see how that makes the height = radius.

    Edit: never mind I figured out what you meant.
    Thanks for the help.
    Last edited by swatpup32; March 19th 2009 at 03:38 AM.
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