A train 120m long crosses a bridge of 180m in 20 seconds. Find speed.

How to Calculate Train Speed: A Simple Guide

Ever watched a train go by and wondered how fast it was moving? This guide will show you how to calculate a train's speed. We'll break it down step-by-step, making it easy to understand. Let's solve the classic physics problem of figuring out a train's speed!

Understanding the Problem: Key Elements

The trick to calculating train speed is understanding that the train has to travel a certain distance to fully cross a bridge.

Here's what we need to know:

• Train Length: How long the train is.
• Bridge Length: How long the bridge is.
• Crossing Time: How long it takes the train to completely cross the bridge.

Imagine the front of the train starts at the beginning of the bridge. The train is *fully* across the bridge only when the back of the train leaves the bridge.

The Formula: Distance, Time, and Speed

The basic formula we'll use is:

Speed = Distance / Time

Let's define the terms:

• Speed: How fast something is moving (e.g., meters per second or kilometers per hour).
• Distance: How far something travels (e.g., meters).
• Time: How long it takes to travel that distance (e.g., seconds).

Important: Make sure your units are consistent! If distance is in meters and time is in seconds, your speed will be in meters per second.

Calculating the Total Distance

To calculate the total distance the train travels, we need to add the train's length and the bridge's length.

Formula: Total Distance = Train Length + Bridge Length

Let's use an example:

• Train Length: 120 meters
• Bridge Length: 180 meters

Total Distance = 120 meters + 180 meters = 300 meters

Plugging in the Values: Solving the Problem

Now, let's use the Speed = Distance / Time formula.

Let's say the crossing time is 20 seconds. We already calculated the total distance is 300 meters.

Calculation: Speed = 300 meters / 20 seconds

Here's how to break it down:

• 300 / 20 = 15

Determining the Speed

The speed of the train is 15 meters per second.

Speed = 15 meters per second

Converting Units (Optional)

Want to make it more relatable? We can convert meters per second to kilometers per hour (Kmph).

15 meters/second is roughly equal to 54 km/h.

Conclusion

You now know how to calculate a train's speed! We took a problem, broke it down to key elements and used the basic formula: Speed = Distance / Time.

Remember the key steps:

1. Understand the problem and identify the lengths and time.
2. Calculate the total distance.
3. Use the speed formula.
4. Determine and state the speed.

Try it out with different train lengths, bridge lengths, and crossing times! See if you can calculate the speeds of some trains you see!