Question

an iron pipe 20 cm long as exterior diameter equal to 25 cm. if the thickness of the pipe is 120 cm. find the whole surface area of the pipe​

Answer 1

The external radius (R)=diameter2⇒252cm

So, the external surface area of the pipe = 2πRl⇒2×227×252×20⇒2200014⇒1571.42cm2

Internal radius (r)=diameter2−1⇒252−1⇒232cm

So, the internal surface area of the pipe = 2πrl⇒2×227×232×20⇒2024014⇒1445.71cm2

Now, the surface area of 2 rings at the corner of the pipe = 2(πR2−πr2)

=2×(227×252×252−227×232×232)=2×(1375028−1163828)=2×(491.07−415.64)=2×75.43=150.86cm2

Total surface area of the pipe is = (total surface area of the external pipe + total surface area of the internal pipe + 2 × surface area of the corner ring).

=(1571.42+1445.71+150.86)cm2=3167.99cm2≈3168cm2

Therefore, we get the total surface area of the pipe as 3168cm2.