A 400 metre long train crosses a man in 20 seconds. Find the speed of the train in km/h.

Options

A. 72 kmph
B. 60 kmph
C. 50 kmph
D. 55 kmph

Answer

To solve the problem of finding the speed of a 400-meter long train that crosses a man in 20 seconds, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Distance**: The length of the train is given as 400 meters. This is the distance that the train travels to completely cross the man.

2. **Identify the Time**: The time taken for the train to cross the man is given as 20 seconds.

3. **Calculate the Speed in Meters per Second**:
- Speed is calculated using the formula:
\[ \text{Speed} = \frac{\text{Distance}}{\text{Time}} \]
- Plugging in the values:
\[ \text{Speed} = \frac{400 \text{ meters}}{20 \text{ seconds}} = 20 \text{ meters/second} \]

4. **Convert Speed to Kilometers per Hour**:
- To convert meters per second to kilometers per hour, we use the conversion factor \( \frac{18}{5} \):
\[ \text{Speed in km/h} = 20 \text{ m/s} \times \frac{18}{5} \]
- Calculating this gives:
\[ \text{Speed in km/h} = 20 \times 3.6 = 72 \text{ km/h} \]

5. **Final Answer**: The speed of the train is 72 km/h.