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Question

The curved surface area of ​​a right circular cylindrical wooden log of uniform density is 440 sq. decimeters. The weight of 1 cubic decimeter of wood is 3 kg and the weight of a log is 18.48 quintals. Find the diameter of the log.

WBBSE Class X Mathematics Right Circular Cylinder 04 Mark 2023

Answer

Given:

  • Curved surface area = 440 sq. decimeters
  • Density of the wood = 3 kg per cubic decimeter
  • Weight of the log = 18.48 quintals (1 quintal = 100 kg)

Convert the weight of the log to kilograms:

Weight of the log = 18.48 × 100 = 1848 kg

Formula for the curved surface area (CSA) of a cylinder:

CSA = 2πrh

Given that CSA = 440:

2πrh = 440 — (1)

Volume of the cylinder:

Volume = πr²h

Weight of the log = Volume × Density

1848 = πr²h × 3

πr²h = 616 — (2)

Divide the second equation by the first:

πr²h \over 2πrh = 616 \over 440

r \over 2 = 14 \over 10

r = 2.8 decimeters

Diameter = 2r = 2 × 2.8 = 5.6 decimeters

Therefore, the diameter of the log is 5.6 decimeters.

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