An iron pipe 20 cm long has external diameter equal
to 25 cm. If the thickness of the pipe is 1 cm, find
the whole surface of the pipe.
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1
Answer:
The pipe is 20cm long (l)
extension diameter is 25cm, thickness is 10m.
∴ exterior radius (R)=
2
25
cm
interior radius (r)=
2
25
−1=
2
23
cm
So, the total surface area is
= exterior surface of the pipe +
interior surface of the pipe +
two ends of the pipe (thickness area)
=2π(R).l+2π(r).l+2(πr
2
−πr
2
)
=2π[l(R+r)+(R+r)(R−r)]
=2π(R+r)(l+R−r)
=2×
7
22
×(
2
25
+
2
23
)(20+
2
25
−
2
23
)
=
7
44
×24×21
=44×72
=3168
So, the total surface face area is 3168 sq.cm.
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