Multiple choice

A roll of newspaper of length 7000 m and thickness 0.022 cm is rolled into a solid cylinder Find its radius

  1. 7 cm

  2. 140 cm

  3. 35 cm

  4. 70 cm
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Volume of paper = length * thickness * width. The problem implies a cylinder of height h = width. Volume = pi * R^2 * h = L * t * h. R^2 = (L * t) / pi = (700000 cm * 0.022 cm) / (22/7) = 15400 * 7 / 22 = 4900. R = 70 cm.

AI explanation

The cross-sectional area of the solid cylinder equals the rectangular cross-section of the unrolled paper, so we use the formula pi * r^2 = length * thickness. Converting the length to 700000 cm allows us to write pi * r^2 = 700000 * 0.022, which simplifies to r^2 = 4900. Taking the square root gives a radius of 70 cm.

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