Math Problem Statement

a cone is made by Rolling a metal sheet in the form of a sector with radius 36 CM are the central angle 150 degree find the curved surface area and the volume of a cone so formed

Solution

To find the curved surface area and volume of the cone formed from a sector, we need to work through the problem step by step.

Given:

  • Radius of the sector (the slant height of the cone, ll) = 36 cm
  • Central angle of the sector = 150°

Step 1: Finding the radius of the cone (rr)

The length of the arc of the sector becomes the circumference of the base of the cone.

  • Arc length of the sector = θ360×2πl\frac{\theta}{360^\circ} \times 2\pi l

Where:

  • θ\theta is the central angle of the sector (150°)
  • ll is the slant height (36 cm)

Substitute the values:

Arc length=150360×2π×36=512×2π×36=30πcm\text{Arc length} = \frac{150^\circ}{360^\circ} \times 2\pi \times 36 = \frac{5}{12} \times 2\pi \times 36 = 30\pi \, \text{cm}

Now, the arc length becomes the circumference of the cone's base:

Circumference of base of the cone=2πr\text{Circumference of base of the cone} = 2\pi r

Equating the arc length and the circumference:

30π=2πr30\pi = 2\pi r

Simplifying:

r=30π2π=15cmr = \frac{30\pi}{2\pi} = 15 \, \text{cm}

Thus, the radius of the cone's base is r=15cmr = 15 \, \text{cm}.

Step 2: Finding the height of the cone (hh)

The slant height ll, radius rr, and height hh of the cone are related by the Pythagorean theorem:

l2=r2+h2l^2 = r^2 + h^2

Substitute the known values:

362=152+h236^2 = 15^2 + h^2

1296=225+h21296 = 225 + h^2

h2=1296225=1071h^2 = 1296 - 225 = 1071

h=107132.72cmh = \sqrt{1071} \approx 32.72 \, \text{cm}

So, the height of the cone is approximately h=32.72cmh = 32.72 \, \text{cm}.

Step 3: Finding the curved surface area of the cone

The curved surface area AA of the cone is given by the formula:

A=πrlA = \pi r l

Substitute the values of r=15cmr = 15 \, \text{cm} and l=36cml = 36 \, \text{cm}:

A=π×15×36=540πcm2A = \pi \times 15 \times 36 = 540\pi \, \text{cm}^2

So, the curved surface area of the cone is 540πcm2540\pi \, \text{cm}^2, or approximately 1696.46cm21696.46 \, \text{cm}^2.

Step 4: Finding the volume of the cone

The volume VV of the cone is given by the formula:

V=13πr2hV = \frac{1}{3} \pi r^2 h

Substitute the values of r=15cmr = 15 \, \text{cm} and h=32.72cmh = 32.72 \, \text{cm}:

V=13π×152×32.72=13π×225×32.72V = \frac{1}{3} \pi \times 15^2 \times 32.72 = \frac{1}{3} \pi \times 225 \times 32.72

V=13×225×32.72×π=2454πcm3V = \frac{1}{3} \times 225 \times 32.72 \times \pi = 2454\pi \, \text{cm}^3

Thus, the volume of the cone is approximately 7707.89cm37707.89 \, \text{cm}^3.

Final Answer:

  • Curved surface area = 540πcm2540\pi \, \text{cm}^2 ≈ 1696.46 cm²
  • Volume = 2454πcm32454\pi \, \text{cm}^3 ≈ 7707.89 cm³

Would you like more details on any step?

Here are some related questions:

  1. What is the formula for the total surface area of a cone?
  2. How does the sector's angle affect the dimensions of the cone?
  3. Can a sector with a different angle form a different cone?
  4. What are the properties of a cone formed by a right circular sector?
  5. How can we find the slant height if the radius and height are known?

Tip: For cones, the slant height is always the longest side when looking at the cross-section triangle formed by height and radius.

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Math Problem Analysis

Mathematical Concepts

Geometry
Surface Area
Volume
Cone
Sector

Formulas

Arc length of sector: (θ/360°) × 2πl
Curved surface area of cone: πrl
Volume of cone: (1/3)πr^2h
Pythagorean theorem: l^2 = r^2 + h^2

Theorems

Pythagorean theorem

Suitable Grade Level

Grades 9-11