math
posted by jean .
what is the weight of a ten foot length of steel pipe? the inside diameter of the pipe is 3/4 of an inch, and the outside diameter i one inch. steel weighs 490lbs. per cubic foot.

area outside = pi (1/2)^2 = pi/4 in^2
area inside = pi (3/8)^2 = 9 pi/64 in ^2
so cross sectional area = .25 pi  .14 pi
= .11 pi in^2
length = 120 in
so
volume = 120*.11 pi = 13.2 pi in^3
then
(13.2 pi in^3) (1 ft^3/12^3 in^3) (490 lb/ft^3
= 3.74 pi lb
=11.76 lb