NCERT Exemplar Solutions
Class 10 - Mathematics - CHAPTER 12: Surface Areas & Volumes - Exercise 12.1
Question 18

Question.  18

The diameters of the two circular ends of a bucket are 44 cm and 24 cm. The height of the bucket is 35 cm. The capacity of the bucket is (in litres)

(A)

32.7 litres

(B)

33.7 litres

(C)

34.7 litres

(D)

31.7 litres

Detailed Answer with Explanation:

Step 1: Identify the shape

The bucket is in the shape of a frustum of a cone (a cone with its top portion cut off).

Step 2: Write the formula for the volume of a frustum

\[ V = \dfrac{1}{3} \pi h (R^2 + Rr + r^2) \] where - \(R\) = radius of the bigger circular end,
- \(r\) = radius of the smaller circular end,
- \(h\) = height of the frustum.

Step 3: Find the radii

Given diameters: 44 cm and 24 cm.

\(R = \dfrac{44}{2} = 22\,\text{cm}\),
\(r = \dfrac{24}{2} = 12\,\text{cm}\).

Step 4: Height

Height of the bucket: \(h = 35\,\text{cm}\).

Step 5: Substitute values in the formula

\[ V = \dfrac{1}{3} \pi (35) (22^2 + 22 \times 12 + 12^2) \]

First calculate inside the brackets:

\(22^2 = 484\),
\(22 \times 12 = 264\),
\(12^2 = 144\).

So, \(484 + 264 + 144 = 892\).

Step 6: Multiply

\[ V = \dfrac{1}{3} \pi (35)(892) \]

\(35 \times 892 = 31,220\).

\[ V = \dfrac{1}{3} \pi (31,220) \]

\(31,220 \div 3 = 10,406.67\).

\[ V \approx 3.1416 \times 10,406.67 = 32,689.1\,\text{cm}^3 \]

Step 7: Convert to litres

We know \(1000\,\text{cm}^3 = 1\,\text{L}\).

\[ V = \dfrac{32,689.1}{1000} = 32.7\,\text{L} \]

Final Answer: The capacity of the bucket is 32.7 litres (Option A).

NCERT Exemplar Solutions Class 10 – Mathematics – CHAPTER 12: Surface Areas & Volumes – Exercise 12.1 | Detailed Answers