A train 180 metres long is running at a speed of 90 km/h. How long will it take to pass a post?
एक 180 मी. लम्बी रेलगाड़ी 90 किमी. प्रति घंटा की गति से चल रही है। एक पोस्ट से गुजरने में वह कितना समय लेगी?

Options

A. `7.8` sec / 7.8 से
B. `8.2` sec / 8.2 से
C. `7.2` sec / 7.2 से
D. 8 sec / 8 से.

Explanation

To solve the problem of how long it will take for a train 180 meters long to pass a post while running at a speed of 90 km/h, we can follow these steps:

### Step 1: Convert the speed from km/h to m/s
The speed of the train is given as 90 km/h. To convert this speed into meters per second (m/s), we use the conversion factor:
\[ 1 \text{ km/h} = \frac{5}{18} \text{ m/s} \]
Thus,
\[ 90 \text{ km/h} = 90 \times \frac{5}{18} \text{ m/s} \]
Calculating this gives:
\[ 90 \times \frac{5}{18} = 25 \text{ m/s} \]

### Step 2: Use the formula for time
To find the time taken to pass the post, we can use the formula:
\[ \text{Time} = \frac{\text{Distance}}{\text{Speed}} \]
In this case, the distance is the length of the train, which is 180 meters, and the speed is 25 m/s.

### Step 3: Calculate the time
Substituting the values into the formula:
\[ \text{Time} = \frac{180 \text{ meters}}{25 \text{ m/s}} \]
Calculating this gives:
\[ \text{Time} = 7.2 \text{ seconds} \]

### Conclusion
The time taken for the train to pass the post is **7.2 seconds**.

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