# An iron pillar consists of a cylindrical portion 2.8 m

Question:

An iron pillar consists of a cylindrical portion 2.8 m high and 20 cm in diameter and a cone 42 cm high is surmounting it. Find the weight of the pillar, given that 1 cubic cm of iron weighs 7.5 gm.

Solution:

Volume of cylindrical portion

$=\pi r^{2} h$

$=\frac{22}{7} \times\left(\frac{20}{2}\right)^{2} \times 280$

$=88000 \mathrm{~cm}^{3}$

Volume of conical portion

$=\frac{1}{3} \pi r^{2} h$

$=\frac{1}{3} \times \frac{22}{7} \times(10)^{2} \times 42$

$=4400 \mathrm{~cm}^{3}$

Total number

$=8800+4400$

$=92400$

So total height

$=92400 \times 7.5$

$=693000 \mathrm{gm}$

$=693 \mathrm{~kg} .$