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.

125^{2} + 125^{2} = 31250

Square root of 31250 = 176.776953 (Diameter)

Radius = 88.38834765

Volume of Cylinder = Pi x 88.38834765^{2} 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?

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

Quote:

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.

125^{2} + 125^{2} = 31250

Square root of 31250 = 176.776953 (Diameter)

Radius = 88.38834765

Volume of Cylinder = Pi x 88.38834765^{2} 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?

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

Quote:

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?

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