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Find the volume of the largest right circular cone that can be cut out of cube having 5 cm as its length of the side.

A21.82

B45.67

C32.72

D65.45

Answer:

C. 32.72

Read Explanation:

Understanding the Geometry

  • A right circular cone is a three-dimensional geometric shape with a circular base and a vertex that is directly above the center of the base.
  • A cube is a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex.

Maximizing Cone Volume within a Cube

  • To cut the largest possible right circular cone from a cube, the cone's base must be inscribed within one of the cube's faces, and the cone's height must be equal to the cube's side length.
  • Diameter of the Cone's Base: The diameter of the largest circle that can be inscribed in a square face of the cube will be equal to the side length of the cube.
  • Radius of the Cone's Base (r): If the side length of the cube is 'a', then the diameter of the cone's base is 'a'. Therefore, the radius (r) = a/2.
  • Height of the Cone (h): The maximum height the cone can have within the cube is equal to the side length of the cube, so h = a.

Formula for the Volume of a Cone

  • The volume (V) of a right circular cone is given by the formula: V = (1/3) * "π" * r^2 * h
  • Where 'r' is the radius of the base and 'h' is the height of the cone.

Applying the Formula to the Given Problem

  • Given side length of the cube (a) = 5 cm.
  • Radius of the cone's base (r) = a/2 = 5/2 cm.
  • Height of the cone (h) = a = 5 cm.
  • Substitute these values into the volume formula:
  • V = (1/3) * "π" * (5/2)^2 * 5
  • V = (1/3) * "π" * (25/4) * 5
  • V = (1/3) * "π" * (125/4)
  • V = (125/12) * "π"

Calculating the Numerical Value

  • Using the approximate value of "π" ≈ 3.14159
  • V ≈ (125/12) * 3.14159
  • V ≈ 10.4167 * 3.14159
  • V ≈ 32.7249...
  • Rounding to two decimal places, the volume is approximately 32.72 cubic centimeters.

Exam Tips

  • Key Ratios: Always remember that for the largest cone in a cube, the radius is half the side length, and the height is equal to the side length.
  • Formula Recall: Be quick to recall the volume of a cone formula.
  • Approximation: For MCQs, often you can estimate "π" as 22/7 or 3.14 to quickly narrow down options if exact calculation isn't needed.
  • Units: Ensure the final answer includes the correct cubic units (e.g., cm³).

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