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A sphere and a cube have …

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A sphere and a cube have the Same surface area.Find the ratio of their volumes.

  • 2 answers

Rashmi Bajpayee 8 years, 10 months ago

According to question

4πr2 = 6a2

r2/a2 = 6/4π.         

r/a = √3/√2π

Now ratio of their volumes

(4/3)πr3 / a3

= 4π/3 × (√3/√2π)3

= (4π/3)(3/2π)(√3/√2π)

= 2(3×7/2×22)

= √21/√11

Therefore ratio of their volumes is √21 : √11

Naveen Sharma 8 years, 10 months ago

Ans. Suppose radius of sphere is r and side of cube is x.

now,

Surface Area of Sphere = Surface Area of Cube

=> \(4 \times \pi \times r^2 = 6 \times x^2\)

=> \({ r^2 \over x^2} = {3 \over 2\pi}\)

=> \({r \over x } = {\sqrt{3 \over 2\pi}}\)

Let volume of Sphere = Vs 

and volume of Cube = Vc

Then

=> \({V_s \over V_c} ={{{ 4 \over 3 }{ \pi r^3} } \over x^3}\)

=> \( {{4 \over 3 }\pi {({r \over x})^3}}\)

=> \( {{4 \pi \over 3} \times {3 \over 2\pi } \times \sqrt{3 \over 2\pi }}\)

=> \( \sqrt{12\over 2\pi}\)

=> \({{ \sqrt 6} \over {\sqrt \pi}}\)

So Required Ratio is = \(\sqrt 6 : \sqrt \pi \)

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