Question:
A boy makes a cone of diameter 28 cm without a base. He then cuts a smaller cone of diameter 20 cm from the cone. He used the bottom part as a lampshade. If the height of the lampshade is 11cm,
(a) find the volume of the whole cone.
(b) find in cm2, the area of the material used to make the lampshade.
Answer:
(a) V ≈ 16420.1
(b) A ≈ 2690.1 cm²
Explanation:
Solution for (a)
Formula: The formula for the volume of a cone is V = 1/3 hπr².
V= πr² h /3 = π × 28/ 2 × 20/ 3 ≈ 16420.0576
16420.0576 in nearest tenths is 16420.1
Therefore, the volume of the whole cone is 16420.1 cm²
Solution for (b)
Formula: A = πrl + πr2.
l = r² + h²
Solving for A
A = πr (r + h²+ r²) = π × 20 × (20 + 112 + 202) ≈ 2690.80077
2690.80077 In nearest tenths, is 2690.1
Therefore, the area of the material used to make the lampshade is 2690.1 cm²