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I iron pipe has a cross section, the iron being 1cm thick.
The mass of 1cm3 of cast iron is 7.2g.
Calculate the mass of a 2metre length of the pipe
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To solve the problem, multiply the cast iron density of 7.2 g/cm^3 by the volume of the metal.
To find the volume of the metal, multiply the cross-section area of the pipe by its length
in consistent units.
To find the area of the cross-section of the pipe, from the greater area of the circle subtract
the area of the smaller circle.
To find the areas of circles in cross-section, the radii or diameters are needed
(since the thickness of the pipe is given, any one of the two radii/diameters should be given).
But neither radius nor diameter of the pipe is given in the post, making the problem like
a three-leg horse.
I am very disappointed by inaccuracy of the person, who created this three-leg horse problem
and disseminates it in the Internet.
It is inappropriate level to communicate with the tutors, posting them crippled tasks.