Q.

Diameter of cylinder A is 7 cm, and the height is 14 cm. Diameter of cylinder B is 14 cm and height is 7 cm. Without doing any calculations can you suggest whose volume is greater? Verify it by finding the volume of both the cylinders. Check whether the cylinder with greater volume also has greater surface area?

NCERT Solutions for Class 8 Maths Chapter 11 Mensuration Ex 11.4 Q2

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Detailed Solution

Volume of cylinder B is greater than A.

For cylinder A, 

Diameter = 7 cm, Radius = 72cm and Height = 14 cm

 Volume of cylinder A = πr2h = (227 )×(72)×(72)×14 = 539 cm3

For cylinder B, 

Diameter = 14 cm, Radius = 7 cm and Height = 7 cm

 Volume of cylinder B = πr2h = (227 )×(7)×(7)×7 = 1078 cm3

Hence, Volume of cylinder B is greater than A.

Surface area of cylinder A = 2πr(r+h ) = 2 x 227 x 72 x (72 + 14) = 385 cm2

Surface area of cylinder B = 2πr(r+h ) = 2 x 227 x 7 x (7 + 7) = 616 cm2

Yes,  the cylinder with greater volume also has greater surface area.

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