A circular ring has an inner radius of 10 cm and outer radius of 20 cm. A point P is taken on its inner boundary and a point Q is taken on its outer boundary such that P, Q and centre of ring are collinear. Another point R is taken on the outer boundary such that PR = 2PQ. With PR as radius, a sphere is formed. What will be the volume of the sphere (in cubic cm)?
Solution
Correct Answer: Option C
Let centre of ring be N.
A point P is taken on its inner boundary and a point Q is taken on its outer boundary such that P, Q and centre of ring are collinear.
⇒ PQ = QN – PN = 20 cm – 10 cm = 10 cm
⇒ PR = 2PQ = 20 cm
Volume of sphere = (4/3) × 3.14 × 20 × 20 × 20 = 33493.33 cubic cm
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