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Ayushree
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Asked: 2026-10-06T04:24:26+00:00 In:

Suppose the Earth is perfectly spherical. A string is wrapped tightly around the equator of the Earth. Another string, 1 metre longer, is placed around the Earth so that it forms a larger circle, staying the same distance above the ground everywhere. How high above the ground is the second string? Repeat this for: (i) the Moon (ii) Jupiter (iii) a volleyball. Are you surprised by the three answers? Why or why not?

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The height is 1 / (2π) ≈ 0.16 m (about 16 cm) for all cases, because radial difference Δr = ΔC / (2π) depends only on added length, entirely independent of the sphere’s radius.

Ganita Manjari Part 2  Class 9 Chapter 14 Step by Step Solutions
Class 9 Chapter 14 Math of Space Surface Area and Volume (Ganita Manjari 2) Solutions

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    1. Let original circumference be C = 2πR and new circumference be C + 1 = 2π(R + h). Subtracting gives 2πh = 1, so the height above ground is h = 1 / (2π) ≈ 0.159 m ≈ 16 cm. This value remains identical for the Moon, Jupiter and a volleyball because radius cancels out completely. The result is counter-intuitive but mathematically expected since height depends solely on the additional string length.

       

      For more NCERT Solutions of Class 9 Maths Ganita Manjari Part 2 Chapter 14 Math of Space: Surface Area and Volume Question Answer (2026-27)

      https://www.tiwariacademy.com/ncert-solutions/class-9/maths/ganita-manjari-chapter-14/

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