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Help Neede On Related Rates (conical Cistern)

  1. Jul 30, 2006 #1
    At a rate of 8ft^3/min, water is pouring into a conical cistern, if the height of a cistern is 12ft and the radius of it's circular opening is 6ft, how fast is the water level rising when the water is 4ft deep?
  2. jcsd
  3. Jul 30, 2006 #2


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    Having someone do the problem for you is not "help". What have you done? Do you know the equation for the volume of a cone in terms of height and radius? Do you see the relationship between height and radius of the water at any time in a cistern that is "12 ft high and radius 6 ft"? (draw a picture and think "similar triangles".)

    Do you know how to go from a "static" formula (volume of cone) to a "rates" formula (how fast volume is changing)?
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