The radius of a wheel is 21 cm. What is the distance (in cm) travelled by the wheel in 10 revolutions ?

Options

A. 660
B. 1320
C. 1980
D. 2640

Answer

To find the distance travelled by the wheel in 10 revolutions, we need to calculate the circumference of the wheel first and then multiply it by the number of revolutions.

### Step-by-Step Solution:

1. **Identify the radius of the wheel**:
- Given radius \( r = 21 \) cm.

2. **Calculate the circumference of the wheel**:
- The formula for the circumference \( C \) of a circle is given by:
\[ C = 2 \pi r \]
- Substituting the value of \( r \):
\[ C = 2 \times \pi \times 21 \]

3. **Use the value of \( \pi \)**:
- For calculations, we can use \( \pi \approx \frac{22}{7} \).
- Thus, substituting \( \pi \):
\[ C = 2 \times \frac{22}{7} \times 21 \]

4. **Simplify the expression**:
- First, calculate \( 2 \times 21 = 42 \):
\[ C = \frac{22 \times 42}{7} \]

5. **Divide 42 by 7**:
- \( 42 \div 7 = 6 \):
\[ C = 22 \times 6 \]

6. **Calculate the circumference**:
- \( 22 \times 6 = 132 \):
\[ C = 132 \text{ cm} \]

7. **Calculate the distance travelled in 10 revolutions**:
- The distance travelled \( D \) is given by:
\[ D = C \times \text{number of revolutions} \]
- Substituting the values:
\[ D = 132 \times 10 \]

8. **Final calculation**:
- \( 132 \times 10 = 1320 \):
\[ D = 1320 \text{ cm} \]

### Conclusion:
The distance travelled by the wheel in 10 revolutions is **1320 cm**.

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