Multiple choice

A solid cylinder of radius 21 cm and height 10 cm is melted and formed into a rod of the square cross-section of side 3 cm. Find the length of the rod.

  1. 1540 cm

  2. 13 m

  3. 15.5 m

  4. 1470 cm
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A Correct answer
Explanation

Volume of cylinder = πr²h = π × 21² × 10 = π × 441 × 10 = 4410π cm³. Volume remains same when melted. Rod has square cross-section with side 3 cm, so area = 9 cm². Length = Volume / Area = 4410π / 9 = 490π cm. Using π ≈ 22/7: 490 × 22/7 = 70 × 22 = 1540 cm.

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