A spherical metal of radius 10 cm is molten and made into 1000 smaller spheres of equal sizes. In this process the surface area of the metal is increased by:

  1. 1000 times
  2. 100 times
  3. 9 times
  4. No change

Answer (Detailed Solution Below)

Option 3 : 9 times

Detailed Solution

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Formula Used:

Volume of sphere = \(\frac{4}{3}\)πr3

Surface area of sphere = 4πr2

Calculation:

If the radius of a smaller sphere be 'r cm' then

Acoording to the question:

\(\frac{4}{3}\)π(10)3 = 1000\(\frac{4}{3}\)π(r)3

r = 1 cm

Surface area of the larger sphere = 4π(10)2 = 400π

Total surface area of 1000 smaller spheres = 1000 × 4π(1)2 = 4000π

Net increase in the surface area = 4000π − 400π = 3600π

Hence, surface area of the metal is increased by 9 times.

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