Question Details

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

Options

A

1125 π

B

750 π

C

1125 π√2

D

750 π √2

Show Answer

Correct Answer :

Option C

1125 π√2

Solution :

The correct option is 1125 π√2.

Let the dimensions (length, width, and height) of the inscribed rectangular box be represented by x, y, and z.

We are given the following information about the rectangular box:
1. The sum of the lengths of all its edges is 144 cm.
2. The total surface area of the box is 846 sq cm.

Step 1: Express the sum of the dimensions
A rectangular box has 12 edges in total (4 lengths, 4 widths, and 4 heights). Therefore, the sum of all its edges is:
4(x+y+z)=144
Dividing both sides by 4 gives:
x+y+z=36

Step 2: Express the total surface area
The total surface area of a closed rectangular box is given by:
2(xy+yz+zx)=846

Step 3: Relate the box dimensions to the sphere's radius
Since the rectangular box is inscribed in a sphere of radius R, the space diagonal of the box is equal to the diameter of the sphere (2R). Using the 3D Pythagorean theorem, the space diagonal is:
x2+y2+z2=2R
Squaring both sides, we get:
x2+y2+z2=4R2

We can find the value of x2+y2+z2 using the algebraic identity:
(x+y+z)2=x2+y2+z2+2(xy+yz+zx)
Substituting the known values from Steps 1 and 2:
362=4R2+846
1296=4R2+846
Subtract 846 from both sides:
4R2=450
Solve for R2:
R2=4504=2252
Taking the square root of both sides gives the radius of the sphere:
R=152

Step 4: Calculate the volume of the sphere
The volume V of a sphere is given by:
V=43πR3
Substitute the radius R=152:
V=43π1523
V=43π337522
Simplifying the constant terms:
V=4×337562π=1350062π=22502π
Multiply the numerator and denominator by 2 to rationalize the denominator:
V=225022π=1125π2

Therefore, the volume of the sphere is 1125 π√2 cubic cm.

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