Question

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 1by2 of the steel actually used was wasted in making the tank.

Answer 1

hlo

1. CSA of cyclinder = 2πrh
diameter = 4.2
radius = 2.1 ( radius is half of diameter)
height = 4.5

2 × 22/7 × 2.1 × 4.5

2× 22 × 0.3 × 4.5

59.4 m

Answer 2

AnswEr:

We have,

Lateral Curved surface area :

$\hookrightarrow \sf \: 2 \times \frac{22}{7} \times 2.1 \times 4.5 \\ \\ \hookrightarrow \sf \: 59.4 \: {m}^{2}$

Let the actual area of the steel used be x m². Then,

Area of steel wasted in making the tank = $\sf\dfrac{x}{12}\:m^2$

$\therefore$ Area of steel present in the tank :

$= \sf \: x - \frac{x}{12} \: {m}^{2} \\ \\ = \sf \: \frac{11x}{12 } \: {m}^{2}$

Hence, $\sf\dfrac{11x}{12}$ = Total surface area of tank .

$\hookrightarrow \sf \: x = \frac{12}{11} \times total \: surface \: area \: of \: tank \\ \\ \hookrightarrow \sf x = \frac{12}{11} \times 2 \times 2.1 \times (4.5 + 2.1) \\ \\ \implies \sf 95.04 \: {m}^{2}$