Volume, Weight 2

[Guest]

A hollow cylindrical iron pillar has the following dimensions:

External diameter - 6 inches
Internal diameter - 4 inches
Length - 12 feet

Grade of iron used weighs 441 lbs. per cu. ft.

Calculate volume and weight of pillar.


Check my calculation:

Volume - pi (R + r) (R - r) h

R - external radius
r - internal radius
h - height or length of cylinder


V - pi (.25 + .166) (.25 - .166) 12
V - pi (.416) (.084) 12
V - 3.1416 x .416 x .084 x 12
V - 1.31736 cu. ft.

Weight - 1.31736 x 441 = 580.955 = 581 lbs.

[Guest]

Yes, your answer is correct

[Guest]

Thank you.

I have a question:

Using specific gravity to calculate weight:

Volume - 1.31736 cu. ft.

Cu. ft. of water = 62.5 lbs.

Weight of cu. ft. of iron - 62.5 x 7.8 (specific gravity of iron) = 487.5 lbs.

Weight of pillar - 487.5 x 1.31736 = 642.213 = 642 lbs.

Should the answer be closer to the other ?

[Guest]

First question used.........
Grade of iron used weighs 441 lbs. per cu. ft.

Second question used......
Weight of cu. ft. of iron - 62.5 x 7.8 (specific gravity of iron) = 487.5 lbs. per cu ft

[Guest]

I was calculating the total weight instead of cu. ft... My error....