Maths question from Social Forest Worker exam, 2026 by JKSSB
A solid metallic sphere of radius R is melted and recast into n identical small solid spheres of radius r. Let S be the surface area of the original large sphere and s be the sum of the surface areas of all n small spheres. Identify the single correct relationship between s and S:
Last updated Jul 21, 2026
Correct Answer:
Option B —
s = n ^ (1/3) * S
To find the relationship between the surface area of the original sphere and the combined surface area of the smaller spheres, we look at volume conservation:
Volume Conservation:
The total volume remains unchanged during melting. The volume of the large sphere equals n times the volume of one small sphere. Since volume depends on the cube of the radius, the cube of the large radius R equals n multiplied by the cube of the small radius r. Taking the cube root, the large radius R equals the small radius r multiplied by n raised to the power of one-third. Therefore, the ratio of the large radius R to the small radius r is n raised to the power of one-third.
Surface Area Comparison:
Surface area depends on the square of the radius. The surface area S of the large sphere is proportional to the square of R. The surface area of a single small sphere is proportional to the square of r, so the sum of the surface areas s of all n small spheres is n multiplied by the square of r.
Ratio of Surface Areas:
Dividing the total small surface area s by the large surface area S gives n multiplied by the square of the ratio of r to R. Since R divided by r equals n raised to the power of one-third, r divided by R equals one divided by n raised to the power of one-third. Squaring this fraction gives one divided by n raised to the power of two-thirds.
Final Relation:
Multiplying n by one divided by n raised to the power of two-thirds simplifies to n raised to the power of one-third (since one minus two-thirds equals one-third).
Thus, the sum of the surface areas s equals n raised to the power of one-third multiplied by S.
Answer verified by Quintessence Classes faculty — Karan Nagar, Srinagar.