This is the important question this question was asked in 2003 cbse board exam. This question number 20 in RS Aggarwal book in exercises 17A chapter volume and surface area of solid.
A wooden article was made by scooping out a hemisphere from each end of a cylinder, as shown in the figure. If the height of the cylinder is 20 cm and its base is of diameter 7 cm, find the total surface area of the article when it is ready.
The height h of cylinder = 20 cm
diameter of its base = 7 cm.
The radius r of its base = 3.5 cm.
Curved surface area of cylinder = 2πrh
= 2 × [22/7] ×3. 5 ×20
= 440 cm²
Now, curved surface area of one hemisphere = 2πr²
= 2 × [22/7] × (3. 5)²
= 77 cm².
Total surface area of the article = Curved surface area of cylinder + 2 [curved surface area of hemisphere]
= 440 +2(77)
= 440 +154
= 594 cm²
∴ Total surface area of the article when it is ready is 594 cm²