Rectangular Box Inscribed in Sphere

CAT 2024 Slot 1 · QA · Hard · Mensuration

The surface area of a closed rectangular box, which is inscribed in a sphere, is 846 sq cm , and the sum of the lengths of all its edges is 144 cm . The volume, in cubic cm , of the sphere is

  1. A.

    750\pi

  2. B.

    1125\pi\sqrt{2}

  3. C.

    1125\pi

  4. D.

    750\pi\sqrt{2}

Answer

B

Explanation

Let box dimensions be a,b,ca, b, c.

  • Surface area 2(ab+bc+ca)=8462(ab + bc + ca) = 846
  • Edge length sum 4(a+b+c)=144    a+b+c=364(a + b + c) = 144 \implies a + b + c = 36

(a+b+c)2=a2+b2+c2+2(ab+bc+ca)(a + b + c)^2 = a^2 + b^2 + c^2 + 2(ab + bc + ca) 362=a2+b2+c2+846    a2+b2+c2=1296846=45036^2 = a^2 + b^2 + c^2 + 846 \implies a^2 + b^2 + c^2 = 1296 - 846 = 450

For a box inscribed in a sphere, diagonal =2R=a2+b2+c2=450=152= 2R = \sqrt{a^2 + b^2 + c^2} = \sqrt{450} = 15\sqrt{2}. Radius of sphere R=1522R = \frac{15\sqrt{2}}{2}.

Volume=43πR3=43π(1522)3=43π3375×228=1125π2\text{Volume} = \frac{4}{3}\pi R^3 = \frac{4}{3}\pi \left(\frac{15\sqrt{2}}{2}\right)^3 = \frac{4}{3}\pi \frac{3375 \times 2\sqrt{2}}{8} = 1125\pi\sqrt{2}

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