Results 1 to 4 of 4

Math Help - Help on one problem please!

  1. #1
    Junior Member
    Joined
    Sep 2008
    Posts
    34

    Mass of air in a cylinder, need help!

    A certain tower has a mass of 7.2 million kilograms and a height of 324 meters. Its base is square with a side length of 125 meters. The steel used to make the tower occupies a volume of 930 cubic meters. Air has a density of 1.225 kg per cubic meter. Suppose the tower was contained in a cylinder. Find the mass of the air in the cylinder. (Assume the dimensions of the cylinder minimize the volume. Round your answer to three decimal places.)
    I know to find its mass = density x (volume of cylinder - volume of tower) but I just can't get to the right answer.

    1252 + 1252 = 31250
    Square root of 31250 = 176.776953 (Diameter)
    Radius = 88.38834765
    Volume of Cylinder = Pi x 88.388347652 x 324 = 7952156.404
    Volume of Cylinder (7,952,156.404) - Volume of Tower (5,062,500) = 2,889,656.404
    2,889,656.404 x 1.225 (Air density) = Mass of air = 3,539,829.095

    However its not the right answer, what am I doing wrong?
    Last edited by Phresh; September 30th 2012 at 12:13 PM.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    skeeter's Avatar
    Joined
    Jun 2008
    From
    North Texas
    Posts
    11,685
    Thanks
    446

    Re: Mass of air in a cylinder, need help!

    Quote Originally Posted by Phresh View Post
    A certain tower has a mass of 7.2 million kilograms and a height of 324 meters. Its base is square with a side length of 125 meters. The steel used to make the tower occupies a volume of 930 cubic meters. Air has a density of 1.225 kg per cubic meter. Suppose the tower was contained in a cylinder. Find the mass of the air in the cylinder. (Assume the dimensions of the cylinder minimize the volume. Round your answer to three decimal places.)
    I know to find its mass = density x (volume of cylinder - volume of tower) but I just can't get to the right answer.

    1252 + 1252 = 31250
    Square root of 31250 = 176.776953 (Diameter)
    Radius = 88.38834765
    Volume of Cylinder = Pi x 88.388347652 x 324 = 7952156.404
    Volume of Cylinder (7,952,156.404) - Volume of Tower (5,062,500) = 2,889,656.404
    2,889,656.404 x 1.225 (Air density) = Mass of air = 3,539,829.095

    However its not the right answer, what am I doing wrong?
    ... did you subtract the correct volume of the tower?
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Sep 2008
    Posts
    34

    Re: Mass of air in a cylinder, need help!

    Quote Originally Posted by skeeter View Post
    ... did you subtract the correct volume of the tower?
    Well I found the volume of the tower by doing lengthxwidthxheight which was 125x125x324, did I approach this wrong?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor
    skeeter's Avatar
    Joined
    Jun 2008
    From
    North Texas
    Posts
    11,685
    Thanks
    446

    Re: Help on one problem please!

    the tower is not a 125x125x324 solid steel structure ... the problem statement told you the volume of steel used in building the tower is 930 m^3
    Follow Math Help Forum on Facebook and Google+

Search Tags


/mathhelpforum @mathhelpforum