Q1: A hollow iron pipe is 21 cm long and its external diameter is 8 cm. If the thickness of the pipe is 1 cm and iron weighs 8 g/cm3, then the weight of the pipe is:
A
3.6 kg
B 36 kg
C
3.696 kg
D 36.9 kg
ANS:B -
3.696 kg
External radius = 4 cm,
Internal radius = 3 cm.
Volume of iron
=
22
x [(4)2 - (3)2] x 21
cm3
7
=
22
x 7 x 1 x 21
cm3
7
= 462 cm3.
Weight of iron = (462 x 8) gm = 3696 gm = 3.696 kg.
cm3
Weight of iron = (462 x 8) gm = 3696 gm = 3.696 kg.