Question

A train of length 200 m is moving with a speed of 72 km/h. How much time will it take to cross a bridge of length 400 m ?

• A. 25 sec
• B. 28 sec
• C. 30 sec
• D. 20 sec

Answer 1

Answer:

C. 30 sec

The train will take 30 seconds to cross the bridge.

## 1. Calculate Total Distance

To completely cross the bridge, the train must travel its own length plus the length of the bridge.

$\text{Total Distance} = \text{Length of Train} + \text{Length of Bridge}$

$\text{Total Distance} = 200\text{ m} + 400\text{ m} = 600\text{ m}$

## 2. Convert Speed to Meters per Second

The speed is given in $\text{km/h}$, but the distance is in meters. Multiply by $\frac{5}{18}$ to convert to $\text{m/s}$.

$\text{Speed} = 72 \times \frac{5}{18}\text{ m/s}$

$\text{Speed} = 4 \times 5 = 20\text{ m/s}$

## 3. Calculate Time Required

Divide the total distance by the speed to find the time.

$\text{Time} = \frac{\text{Total Distance}}{\text{Speed}}$

$\text{Time} = \frac{600\text{ m}}{20\text{ m/s}} = 30\text{ seconds}$

Final Answer

The total time required for the train to cross the bridge is exactly 30 seconds.