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A cylindrical rod whose height is 8 times of its radius is melted and recast into spherical balls of same radius. The number of balls will be

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Question

A cylindrical rod whose height is 8 times of its radius is melted and recast into spherical balls of same radius. The number of balls will be

Options

  • 4

  • 3

  • 6

  • 8

MCQ
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Solution

In the given problem, we have a cylindrical rod of the given dimensions:

Radius of the base (rc) = x units

Height of the cylinder (h) = 8x units

So, the volume of the cylinder (Vc) =  ` pi r^2 h`

`= pi x^2 (8x) `

`= 8 pi x^3`

Now, this cylinder is remolded into spherical balls of same radius. So let us take the number of balls be y.

Total volume of y spheres (Vs) = `y(4/3 pi r^3) `

=`y(4/3 pi x^3)`

So, the volume of the cylinder will be equal to the total volume of y number of balls.

We get,  `V_c = yV_s`

`8 pi x^3 = y (4/3 pi x^3)`

        ` 8 = 4/3 y`

        ` y = ((8)(3))/4`

          y = 6

Therefore, the number of balls that will be made is 6 . 

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Chapter 21: Surface Areas and Volume of a Sphere - Exercise 21.4 [Page 26]

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R.D. Sharma Mathematics [English] Class 9
Chapter 21 Surface Areas and Volume of a Sphere
Exercise 21.4 | Q 6 | Page 26

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