Question

Find the height of frustum of cone if slant height is 10 cm and radius of circular section are 15 cm and 9 cm respectively.
1. 6 cm
2. 8 cm
3. 9 cm
4. 10 cm

Answer 1

Correct Answer - Option 2 : 8 cm

Given:

Slant height, L = 10 cm

Radius of bigger circular section, R = 15 cm

Radius of smaller circular section, r = 9 cm

Formula used:

Slant height, L = √(h² + (R – r)²)

Calculation:

Slant height, L = √(h2 + (R – r)2)

⇒ 10 = √(h² + (15 – 9)²)

Squaring on both side

⇒ 100 = h² + 6²

⇒ h² = 100 – 36

⇒ h² = 64

⇒ h = 8 cm

∴ The height of frustum of cone is 8 cm