A train `200` metres long is running at a speed of `20` metre per second. In how much time (in second) it will cross a bridge of `400` metre long ?

Options

A. `20`
B. `25`
C. `30`
D. `60`

Answer

To solve the problem, we need to determine how long it takes for a train to cross a bridge. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the lengths involved
- The length of the train is **200 meters**.
- The length of the bridge is **400 meters**.

### Step 2: Calculate the total distance to be covered
To completely cross the bridge, the train must cover its own length plus the length of the bridge. Therefore, the total distance \( D \) is:
\[ D = \text{Length of the train} + \text{Length of the bridge} = 200 \text{ meters} + 400 \text{ meters} = 600 \text{ meters} \]

### Step 3: Identify the speed of the train
The speed of the train is given as **20 meters per second**.

### Step 4: Use the formula for time
The formula to calculate time \( T \) is:
\[ T = \frac{D}{S} \]
where \( D \) is the distance and \( S \) is the speed.

### Step 5: Substitute the values into the formula
Substituting the values we have:
\[ T = \frac{600 \text{ meters}}{20 \text{ meters/second}} = 30 \text{ seconds} \]

### Conclusion
The time taken for the train to cross the bridge is **30 seconds**.

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