class 9 chapter 13 exersice 13.2 ncert quesrion 1,3
Answers
Answer:
1. The curved surface area of a right circular cylinder of height 14 cm is 88 cm2. Find the diameter of the base of the cylinder. (Assume π =22/7 )
Solution:
Height of cylinder, h = 14cm
Let the diameter of the cylinder be d
Curved surface area of cylinder = 88 cm2
We know that, formula to find Curved surface area of cylinder is 2πrh.
So 2πrh =88 cm2 (r is the radius of the base of the cylinder)
2×(22/7)×r×14 = 88 cm2
2r = 2 cm
d =2 cm
Therefore, the diameter of the base of the cylinder is 2 cm.
3. A metal pipe is 77 cm long. The inner diameter of a cross section is 4 cm, the outer diameter being 4.4cm. (see fig. 13.11). Find its
(i) inner curved surface area,
(ii) outer curved surface area
(iii) total surface area
(Assume π=22/7)
Solution:
Let r1 and r2 Inner and outer radii of cylindrical pipe
r1 = 4/2 cm = 2 cm
r2 = 4.4/2 cm = 2.2 cm
Height of cylindrical pipe, h = length of cylindrical pipe = 77 cm
(i) curved surface area of outer surface of pipe = 2πr1h
= 2×(22/7)×2×77 cm2
= 968 cm2
(ii) curved surface area of outer surface of pipe = 2πr2h
= 2×(22/7)×2.2×77 cm2
= (22×22×2.2) cm2
= 1064.8 cm2
(iii) Total surface area of pipe = inner curved surface area+ outer curved surface area+ Area of both circular ends of pipe.
= 2r1h+2r2h+2π(r12-r22)
= 9668+1064.8+2×(22/7)×(2.22-22)
= 2031.8+5.28
= 2038.08 cm2
Therefore, the total surface area of the cylindrical pipe is 2038.08 cm2.
PLZ MARK ME BRAINLIEST