A person driving a car with a speed 72 km/h suddenly sees a boy crossing the road. If the distance moved by car, before the person applies brakes is 5 m, the reaction time of the person is

Options

A. 0.5 s
B. 0.10 s
C. 10 s
D. 0.25 s

Answer

To solve the problem, we need to determine the reaction time of a person driving a car who sees a boy crossing the road. The car travels a distance of 5 meters before the driver applies the brakes. The speed of the car is given as 72 km/h.

### Step-by-Step Solution:

1. **Convert the speed from km/h to m/s:**
\[ \text{Speed in m/s} = \text{Speed in km/h} \times \frac{1000 \text{ m}}{3600 \text{ s}} = 72 \times \frac{1000}{3600} = 20 \text{ m/s} \]

2. **Identify the distance traveled during the reaction time:**
The distance moved by the car before the driver applies the brakes is given as 5 meters.

3. **Use the formula for time:**
The time taken (reaction time) can be calculated using the formula:
\[ \text{Time} = \frac{\text{Distance}}{\text{Speed}} \]
Here, the distance is 5 meters and the speed is 20 m/s.

4. **Calculate the reaction time:**
\[ \text{Reaction Time} = \frac{5 \text{ m}}{20 \text{ m/s}} = 0.25 \text{ seconds} \]

### Conclusion:
The reaction time of the person driving the car is **0.25 seconds**.

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