(Q7).An iron pillar consists of a Cylindrical portion of 2.8 m height and 20 cm in diameter and a cone of 42 cm height surmounting it. Find the weight of the pillar if 1 cm3 of iron weighs 7.5 g.

.42 cm2.8m10 cm

Volume of the iron pillar = Volume of the cylinder + Volume of the cone

Cylinder:

Radius =
d
2
 =
= cm

Height = 2.8 m = cm

Volume = πr2h

=
× × ×

= cm3

Cone:

Radius ‘r’ =
d
2
 =
= cm

height ‘h’ = 42 cm

Volume =
1
3
 πr2h
=
×
× × ×

= cm3

∴ Total volume = + = cm3

∴ Total weight of the pillar at a weight of 7.5 g per 1 cm3 = 92400 × 7.5

= gms

=
kg

= kg.