NumericalModerate3 marks
A certain number of metallic cones, each of radius 2 cm and height 3 cm are melted and recast into a solid sphere of radius 6 cm. Find the number of cones.
Topic: Mensuration of solids
Previous-year question practice database
Answer
Exam answer
Radius of each cone = 2 cm Height of each cone = 3 cm Radius of sphere = 6 cm
Volume of one cone = (1/3)πr²h
= (1/3)π(2)²(3)
= 4π cm³
Volume of sphere = (4/3)πR³
= (4/3)π(6)³
= 288π cm³
Let the number of cones be n.
Since the cones are melted and recast into the sphere:
n × 4π = 288π
n = 72
Answer:
72 cones.
Explanation
Melting and recasting do not change the volume of metal. Therefore the total volume of all the cones equals the volume of the sphere.
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