Question

A hellow iron Pipe, which is 14cm long and has its external diameter 10cm. If the thickness of the pipe is 2cm and iron weighs 10g/cm3, find the weight of the pipe?

Answer 1

We know that volume of hollow pipe = Outer volume - Inner volume
According to the question, we get :-
πr²h - π(r-2)²h [As the inner radius of the pipe is 2cm less than the outer radius]
= (22/7 x 5 x 5 x 14) - (22/7 x 3 x 3 x 14) 
= 1100 - 396
= 704 cm³

Now the weight of 1 cm³ of iron is 10gm. Thus weight of pipe 
= 704 x 10
= 7040 gm 
= 7kg 40gm

Hope that helps !!

Answer 2

vol.of a hollow pipe= pi×R²×h-pi×r²×h= pi*h(R²-r²)
here,R=5cm,r=5-2=3cm
thus vol.=22/7×14×(5²-3²)
             =704cm³
it is given that each cm³ of iron weighs 10g.
hence,the weight of 704cm³ of iron= 704×10=7040g
i.e.the weight of the pipe=7040g= 7.04kg