NCERT Class 9 Solutions: Surface Areas and Volumes (Chapter 13) Exercise 13.8 – Part 4

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Volume of sphere=4/3 πr^3

Volume of Sphere

Q-9 Twenty seven solid iron spheres, each of radius and surface area are melted to form a sphere with surface area. Find the

  1. Radius of the new sphere,

  2. Ratio of

Solution:

When the spheres are melted the volume of molten material remains the same.

  1. Volume ofsolid sphere of radius , Volume of the new sphere of radius …………….equation (2), Since the volume must remain the same, therefore,

  2. Required ratio of surface area,

  3. =

  4. or the ratio is

Q-10 A capsule of medicine is in the shape of a sphere of diameter. How much medicine (in) is needed to fill this capsule?

Solution:Diameter of the spherical capsule , Therefore, radius (r) , Medicine needed for filling this capsule = Volume of this spherical capsule