Math Problem Statement

The surface area of a sphere of radius 5 cm is five times the area of the curved surface of a cone of radius 4 cm. Find the height and volume of the cone.

Solution

To solve the problem:

  1. Surface Area of Sphere: The surface area of a sphere is given by: Asphere=4πr2A_{\text{sphere}} = 4\pi r^2 Here, r=5cmr = 5 \, \text{cm}: Asphere=4π(5)2=100πcm2A_{\text{sphere}} = 4\pi (5)^2 = 100\pi \, \text{cm}^2

  2. Curved Surface Area of Cone: Denote the curved surface area of the cone by AconeA_{\text{cone}}. According to the problem: Asphere=5AconeA_{\text{sphere}} = 5 \cdot A_{\text{cone}} Substituting Asphere=100πA_{\text{sphere}} = 100\pi: 100π=5Acone    Acone=20πcm2100\pi = 5 \cdot A_{\text{cone}} \implies A_{\text{cone}} = 20\pi \, \text{cm}^2

    The formula for the curved surface area of a cone is: Acone=πrlA_{\text{cone}} = \pi r l where rr is the radius and ll is the slant height. Substituting r=4cmr = 4 \, \text{cm} and Acone=20πA_{\text{cone}} = 20\pi: 20π=π(4)l    l=5cm20\pi = \pi (4) l \implies l = 5 \, \text{cm}

  3. Height of the Cone: Using the Pythagorean theorem: l2=r2+h2l^2 = r^2 + h^2 Substituting l=5cml = 5 \, \text{cm} and r=4cmr = 4 \, \text{cm}: (5)2=(4)2+h2    25=16+h2    h2=9    h=3cm(5)^2 = (4)^2 + h^2 \implies 25 = 16 + h^2 \implies h^2 = 9 \implies h = 3 \, \text{cm}

  4. Volume of the Cone: The formula for the volume of a cone is: V=13πr2hV = \frac{1}{3} \pi r^2 h Substituting r=4cmr = 4 \, \text{cm} and h=3cmh = 3 \, \text{cm}: V=13π(4)2(3)=13π(16)(3)=16πcm3V = \frac{1}{3} \pi (4)^2 (3) = \frac{1}{3} \pi (16) (3) = 16\pi \, \text{cm}^3

Final Answers:

  • Height of the cone: 3cm3 \, \text{cm}
  • Volume of the cone: 16πcm316\pi \, \text{cm}^3

Would you like detailed explanations or diagrams for this solution?

Related Questions:

  1. How would the answer change if the sphere's radius was doubled?
  2. What happens to the volume of the cone if its height is halved?
  3. How is the relationship between slant height and base radius derived in cones?
  4. What is the general formula for the curved surface area of a cone in terms of height?
  5. How do the formulas for spheres and cones relate in terms of π\pi?

Tip: Always verify your calculations by substituting back into the original conditions!

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Math Problem Analysis

Mathematical Concepts

Geometry
Surface Area
Curved Surface of Cone
Volume of Cone
Pythagorean Theorem

Formulas

Surface area of sphere: 4πr^2
Curved surface area of cone: πrl
Pythagorean theorem: l^2 = r^2 + h^2
Volume of cone: (1/3)πr^2h

Theorems

Pythagorean Theorem

Suitable Grade Level

Grades 9-10