The wheel of a car makes `10 rev//s`. It is stopped in 14 s .Then the number of revolutions it makes before it stops

Options

A. 10
B. 20
C. 40
D. 70

Explanation

To solve the problem of how many revolutions the wheel of a car makes before it stops, we can use the formula for the average angular displacement when the initial and final angular velocities are known.

### Step-by-Step Solution:

1. **Identify the Given Values:**
- Initial frequency of the wheel, \( N_1 = 10 \) revolutions per second (rev/s)
- Final frequency of the wheel, \( N_2 = 0 \) rev/s (since it stops)
- Time taken to stop, \( t = 14 \) seconds

2. **Calculate the Average Frequency:**
The average frequency \( N \) during the time interval can be calculated using the formula:
\[ N = \frac{N_1 + N_2}{2} \]
Substituting the values:
\[ N = \frac{10 + 0}{2} = \frac{10}{2} = 5 \text{ rev/s} \]

3. **Calculate the Total Revolutions:**
The total number of revolutions \( R \) made during the time \( t \) can be calculated using the formula:
\[ R = N \times t \]
Substituting the average frequency and time:
\[ R = 5 \text{ rev/s} \times 14 \text{ s} = 70 \text{ revolutions} \]

4. **Final Answer:**
The wheel makes a total of **70 revolutions** before it stops.