1. ## 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)
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?

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

Originally Posted by Phresh
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)
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?

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

Originally Posted by skeeter
... 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?

4. ## 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