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Math Help - Volume

  1. #1
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    Volume

    I am stuck on this problem and don't know how to begin...

    A right circular cylindrical container is to be built to hold a volume of 500 cubic centimeters. The cost of material used for the top and bottom is $.5/cm^2 and $.3/cm^2 . Use calculus to find the radius and cost of the least expensive container.

    ANY HELP IS MUCH APPRECIATED
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  2. #2
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    A couple of questions to ask yourself - What is the formula for the volume of a circular cone? What is the area of a triangle? What is the area of a circle. Write these down, draw a picture, and see if something doesn't click with how to use those three to answer your question (which as you should know, is an optimization problem, and will involve derivatives).
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  3. #3
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    Quote Originally Posted by ANDS! View Post
    A couple of questions to ask yourself - What is the formula for the volume of a circular cone? What is the area of a triangle? What is the area of a circle. Write these down, draw a picture, and see if something doesn't click with how to use those three to answer your question (which as you should know, is an optimization problem, and will involve derivatives).
    This is what i have so far:
    500=pi*r^2h
    h=500/pi*r^2
    C=$.5(area of top +bottom)+$.3(area of side)
    =.5(pi*r^2+pi*r^2)+.3(pi2rh)
    =pi*r^2+.6pi*r*h
    =pi*r^2+.6r(500/pi*r^2)
    =pi*r^2+300r^-1
    C'=2pi*r-300r^-2
    (0=2pi*r-300r^-2)r^2
    r=(300/2pi)^1/3=(150/pi)^1/3=15.9155 ft.

    and h=(500/pi*r^2)
    =500/pi(150/pi)^2/3
    =(500/pi)*((pi^2/3)/(500^1/3)
    =(500^2/3)/(pi^1/3)=43.01ft

    what do i do next?
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  4. #4
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    Assuming that is correct, now you would simply optimize your function.
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  5. #5
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    Quote Originally Posted by ANDS! View Post
    Assuming that is correct, now you would simply optimize your function.
    Im still unsure as to how to do that
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  6. #6
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    Quote Originally Posted by sydewayzlocc View Post
    This is what i have so far:
    500=pi*r^2h
    h=500/pi*r^2
    C=$.5(area of top +bottom)+$.3(area of side)
    =.5(pi*r^2+pi*r^2)+.3(pi2rh)
    =pi*r^2+.6pi*r*h
    =pi*r^2+.6r(500/pi*r^2)
    =pi*r^2+300r^-1
    C'=2pi*r-300r^-2
    (0=2pi*r-300r^-2)r^2
    r=(300/2pi)^1/3=(150/pi)^1/3=15.9155 ft.

    and h=(500/pi*r^2)
    =500/pi(150/pi)^2/3
    =(500/pi)*((pi^2/3)/(500^1/3)
    =(500^2/3)/(pi^1/3)=43.01ft

    what do i do next?
    Okay, as long as you are sure that is a minimum and not a maximum or saddle, finish the problem by calculating the cost using those values.
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