Question

iron pipe 20 CM long, exterior diameter 25 CM, thickness. 1cm. find whole surface area. ​

Answer 1

Answer :

$h = 20cm \\ r_{1} = \frac{25}{2}cm \: \\ r_{2} = \frac{24}{2} \: or \: 12cm \: \: {since \: thickness \: is \: 1cm} \\ \\ c.s.a = 2\pi r_{1}h + 2\pi r_{2}h \\ c.s.a = 2\pi h( r_{1} + r_{2}) \\ c.s.a = 2 \times \frac{22}{7} \times 20 ( \frac{49}{2}) \\ c.s.a = 44 \times 10 \times 7 \\ c.s.a = 3080 {cm}^{2} \\ \\ area \: of \: two \: rings \: = 2 (\pi {(r_{1})}^{2} - \pi { (r_{2}) }^{2}) \\ = 2 \times \frac{22}{7} \times 12.25 \\ = 44 \times 1.75 \\ = 77 {cm}^{2} \\ \\ total \: area = c.s.a \: + area \: of \: two \: rings \\ area = 3080 + 77 \\ area = 3157 {cm}^{2}$