• Support PF! Buy your school textbooks, materials and every day products via PF Here!

Very basic physics (mechanics) question

  • Thread starter itzela
  • Start date
34
0
A structural I beam is made of steel. A view of its cross-section and its dimensions are shown in Figure P1.11. The density of steel is 7.56 * 10^3 kg/m^3. What is the mass of the section 8.5 m long?

Figure P1.11 (shown below)




I tried doing this by:
1) changing the 8.5 m into cm... giving me 850 cm.
2) getting the volume by parts: 2[15cm(1cm)(1cm)] + [848cm (1cm)(1cm)]
giving me 878 cm^3.
3) I converted into m^3 and got 8.78*10^-4
4) I used the density and then got a mass of 6.38 kg

But it's a wrong answer... any help would be much appreciated!
 

Attachments

Last edited:

Fermat

Homework Helper
872
1
I don't understand how you worked out your volume.

Try simply working out the area of the cross-section and multilpying that by the length.
 
2,208
1
What you want to do is find the surface area of the I beam. Then you know the height of the beam is 850m and its area, so you can find the volume by multiplying the two.

The area is (36*15) - (34*14) if im not mistaken.
 

quasar987

Science Advisor
Homework Helper
Gold Member
4,771
7
how you calculated the volume eludes me. How about 2[15*1*850] + 34*1*850 = 54400 cm^3
 

Related Threads for: Very basic physics (mechanics) question

  • Posted
Replies
4
Views
2K
Replies
5
Views
343
Replies
3
Views
1K
  • Posted
Replies
20
Views
2K
  • Posted
Replies
1
Views
2K
  • Posted
Replies
2
Views
6K
  • Posted
Replies
2
Views
1K
  • Posted
Replies
16
Views
755

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top