5. A cylindrical pillar is 50 cm in diameter and 3.5 m in height. Find the cost of painting
the curved surface of the pillar at the rate of 12.50 per m²
6. Curved surface area of a right circular cylinder is 44 m”. If the radius of the base of the
cylinder is 0.7m, find its height.
1. The inner diameter of a circular well is 3.5 m. It is 10 m deep. Find
(1) its inner curved surface area,
(i) the cost of plastering this curved surface at the rate of 40 per mº,
8. In a hot water heating system, there is a cylindrical pipe of length 28 mand diameter
5 cm. Find the total radiating surface in the system
Answers
(5) ans:- D = 2r
Therefore r = 25 cm
h = 3.5m = 350 cm
C.S.A of cylinder = 2πrh
= 2 × 22/7 × 350 × 50
= 110000 cm^2
= 110000/100×100 m^2
= 11 m^2
cost of painting the pillar = 11 × 12.50 = ₹137.5
(6) ans:- let height be h m
now, C.S.A of cylinder = 2πrh
= 44 = 2 × 22/7 × 0.7 × h
= h = 0.7/7 = . 1 m Or 10 CM
hence, the height of cylinder is 10 CM.
(7) ans:- inner D = 3.5 m
therefore inner radius = 1.75 m
(I) inner C.S.A of well = 2πrh
= 2×22/7×1.75×10
= 44×0.25×10
= 110 m^2
(ii) cost of plastering the C.S.A of well = 110×40=₹4400
(8) ans:- D = 5 CM
r = 2.5 CM Or 0.025m
now,
the total radiating surface = 2πr(r+h)
= 2×22/7×0.025(0.025+28)
= 2×22/7×0.025×28.025
= 30.8275/7 = 4.40m^2 approx