Calculating the mass and number of atoms of a structural I beam

[hsbc2003]

Please add this title: Calculating the mass and number of atoms of a structural I beam.

Homework Statement

A structural I beam is made of iron> A view of its cross-section and its dimensions is shown in the figure, where d = 2 cm, w= 31 cm, h= 28 cm and the length (not shown) of the beam is L= 1.53 m.

The density of iron is 7560 kg/m^3. The atomic weight of iron is 55.85 g/mol and Avagadro number is Na= 6.02214e23/mol.

What is the mass of a section 1.53 m long? (in kg)
How many atoms are there in this section? (in units of atoms)

The Attempt at a Solution

I calculated the volume of the I beam ( (h*w*l)-(the volume of the empty space))
and then I multiply it by the density of iron to get the mass.

but the answer was wrong, thus i I tried to calculate the number of atoms using Avagadro's number the answer will be wrong as well...

I hope you help me calculating the mass...

Thank you

 

[tiny-tim]

small earthquake in Chile … not many goldfish

I calculated the volume of the I beam ( (h*w*l)-(the volume of the empty space))

Hi hsbc2003!

hmm … that's a really weird way to do it …

(and it's very easy to make a mistake that way … always choose a method that's resonably idiot-proof )

Hint: the whole cross-section has the same width (2cm),

so cross-section area A = 2cm x total "length",

and then volume = A x L.

 

[LowlyPion]

I calculated the volume of the I beam ( (h*w*l)-(the volume of the empty space)) and then I multiply it by the density of iron to get the mass.

but the answer was wrong,

Your method looks ok. What numbers did you get? What cross section? Did you keep your units straight?