A car is moving with a velocity 20 m `s^(-1)`. The brakes are applied to retard it at a rate of 2 m `s^(-2)`. What will be the velocity after 5 s of applying the brakes ?.

Explanation

To solve the problem, we will use the formula for final velocity in uniformly accelerated motion:

\[ v = u + at \]

Where:
- \( v \) = final velocity
- \( u \) = initial velocity
- \( a \) = acceleration (or retardation in this case)
- \( t \) = time

### Step-by-step Solution:

1. **Identify the given values:**
- Initial velocity (\( u \)) = 20 m/s
- Retardation (\( a \)) = -2 m/s² (negative because it is a retardation)
- Time (\( t \)) = 5 s

2. **Substitute the values into the formula:**
\[ v = u + at \]
\[ v = 20 + (-2) \times 5 \]

3. **Calculate the product of acceleration and time:**
\[ (-2) \times 5 = -10 \]

4. **Add this value to the initial velocity:**
\[ v = 20 - 10 \]

5. **Calculate the final velocity:**
\[ v = 10 \text{ m/s} \]

### Conclusion:
After applying the brakes for 5 seconds, the velocity of the car will be **10 m/s**.