A diagram shows of a cone with slant height 10.5cm. If the curved surface area of the cone is 115.5cm. calculate correct to (3 sig figure) .
Base radius and height of the cone and volume of the cone.



Answer :

Answer:

To find the base radius, height, and volume of the cone, we'll use the given information and the formulas for the properties of a cone.

1. **Given Data:**

- Slant height (\( l \)) = 10.5 cm

- Curved surface area (CSA) = 115.5 cm²

2. **Formulas:**

- Curved Surface Area (\( \text{CSA} \)) = \(\pi r l\)

- Base radius (\( r \)) = ?

- Height (\( h \)) = ?

- Volume (\( V \)) = \(\frac{1}{3} \pi r^2 h\)

3. **Calculate the Base Radius:**

From the formula for the curved surface area:

\[

\text{CSA} = \pi r l

\]

Substitute the known values:

\[

115.5 = \pi r \times 10.5

\]

Solve for \( r \):

\[

r = \frac{115.5}{\pi \times 10.5}

\]

\[

r = \frac{115.5}{32.98672} \approx 3.50 \text{ cm} \quad \text{(to 3 significant figures)}

\]

4. **Calculate the Height:**

Using the Pythagorean theorem for the right triangle formed by the height, radius, and slant height:

\[

l^2 = r^2 + h^2

\]

Substitute the known values:

\[

10.5^2 = 3.50^2 + h^2

\]

\[

110.25 = 12.25 + h^2

\]

\[

h^2 = 110.25 - 12.25

\]

\[

h^2 = 98

\]

\[

h = \sqrt{98} \approx 9.90 \text{ cm} \quad \text{(to 3 significant figures)}

\]

5. **Calculate the Volume:**

Using the volume formula:

\[

V = \frac{1}{3} \pi r^2 h

\]

Substitute the known values:

\[

V = \frac{1}{3} \pi (3.50)^2 (9.90)

\]

\[

V = \frac{1}{3} \pi (12.25) (9.90)

\]

\[

V = \frac{1}{3} \pi (121.275)

\]

\[

V = \frac{1}{3} \times 3.14159 \times 121.275 \approx 127 \text{ cm}^3 \quad \text{(to 3 significant figures)}

\]

**Summary:**

- Base radius (\( r \)) = 3.50 cm (to 3 significant figures)

- Height (\( h \)) = 9.90 cm (to 3 significant figures)

- Volume (\( V \)) = 127 cm³ (to 3 significant figures)