Question

Question 9
Find:
(i) The lateral or curved surface area of a closed cylindrical petrol storage tank that is 4.2 m in diameter and 4.5 m high.
(ii) How much steel was actually used, if $\frac{1}{12}$ of the steel actually used was wasted in making the tank? $[Assume\pi =\frac{22}{7}]$

Answer 1

(i)
Height (h) of cylindrical tank = 4.5 m
Radius (r) of the circular end of cylindrical tank $=\left(\frac{4.2}{2}\right)m=2.1m$
Lateral or curved surface area of tank $=2\pi rh$
$=(2\times \frac{22}{7}\times 2.1\times 4.5)m^2=(44\times 0.3\times 4.5)m^2=59.4m^2$

(ii)
Total surface area of tank $=2\pi r(r+h)$
$=[2\times \frac{22}{7}(2.1\times (4.5+2.1)\left)\right]m^2=(44\times 0.3\times 6.6)m^2=87.12m^2$
Let A $m^2$ steel sheet be actually used in making the tank.
$\therefore A(1-\frac{1}{12})=87.12m^2\Rightarrow A(\frac{11}{12}\times 87.12)m^2\Rightarrow A=95.04m^2$
Therefore, $95.04m^2$ steel was used in actual while making such a tank.