Listen NCERT Audio Books to boost your productivity and retention power by 2X.
A storage tank consists of a circular cylinder with a hemisphere adjoined on either end. If the external diameter of the cylinder be 1.4 m and its length be 8 m, find the cost of painting it on the outside at the rate of Rs. 10 per m2.
Curved surface area of a cylinder = 2πrh
Curved surface area of hemisphere = 2πr2
Given, external diameter of the cylinder be 1.4 m and its length be 8 m
Thus r = 0.7m and h = 8m
Total curved surface area = 2πrh + 2πr2
⇒ Total curved surface area = 2 × (22/7) × 0.7 × 8 + 2 × (22/7) × 0.72 = 38.28 m2
Cost of painting it on the outside at the rate of Rs. 10 per m2 = 38.28 × 10 = Rs. 382.80
The front compound wall of a house is decorated by wooden spheres of diameter 21 cm, placed on small supports as shown in Fig. 21.11. Eight such spheres are used for this purpose, and are to be painted silver. Each support is a cylinder of a radius 1.5 cm and height 7 cm and is to be painted black. Find the cost of paint required if silver paint costs 25 paise per cm2 and black paint cost 5 paise per cm2.