NCERT Exemplar Solutions
Class 10 - Mathematics - CHAPTER 11: Area Related To Circles - Exercise 11.3
Question 5

Question. 5

A cow is tied with a rope 14 m long at the corner of a rectangular field of dimensions 20 m × 16 m. Find the area it can graze.

Answer:

\(49\pi\;\text{m}^2\) (≈ 153.94 m²)

Detailed Answer with Explanation:

Step 1: Understand the situation.

A cow is tied at the corner of a rectangular field with a rope of length 14 m. This means the cow can move around only in a circular path of radius 14 m, but since it is tied at a corner, it cannot move in all directions — it can move only in one-quarter (1/4) of the circle.

Step 2: Check the field size.

The field has length 20 m and breadth 16 m. Both of these are larger than 14 m (the rope length). So the cow’s full circular movement of radius 14 m fits inside the field boundaries at the corner.

Step 3: Area grazed is a quarter of a circle.

When tied at a corner, the grazed area is a quarter-circle with radius \(r = 14\,\text{m}\).

Step 4: Formula for area of a circle.

The full area of a circle is given by: \(A = \pi r^2\)

Step 5: Quarter of the circle.

Since only 1/4th of the circle is available: \(A = \dfrac{1}{4} \pi r^2\)

Step 6: Substitute values.

\(A = \dfrac{1}{4} \pi (14^2)\)
\(A = \dfrac{1}{4} \pi (196)\)
\(A = 49\pi\;\text{m}^2\)

Step 7: Approximate value.

Using \(\pi ≈ 3.1416\), \(A ≈ 49 × 3.1416 = 153.94\,\text{m}^2\).

Final Answer: The cow can graze an area of \(49\pi\;\text{m}^2\) (≈ 153.94 m²).

NCERT Exemplar Solutions Class 10 – Mathematics – CHAPTER 11: Area Related To Circles – Exercise 11.3 | Detailed Answers