Crossing Time | MCQs

Explanation

Given:

• Length of each train = 150 m

• Total length to cross = 150 m + 150 m = 300 m

• Time taken to cross = 15 seconds

• Trains are moving in opposite directions at the same speed

 Step 1: Use the formula

Relative speed= Total distance/Time ​= 300 / 15​ = 20 m/s

Since both trains have the same speed and are moving in opposite directions:

Relative speed=v+v=2v=20 m/s⇒v=20​/2=10 m/s

Step 2: Convert to km/h

$$1 text{m/s} = 3.6 text{km/h} Rightarrow 10 text{m/s} = 10 times 3.6 = 36 text{km/h}$$

Explanation

When the trains move in opposite directions, their relative speed is the sum of their individual speeds:

60 km/h + 40 km/h = 100 km/h

To convert this to meters per second, divide by 3600 (since there are 3600 seconds in an hour):

100 km/h ÷ 3600 = 27.78 m/s (approximately)

The total distance covered by the trains as they cross each other is the sum of their lengths:

140 m + 160 m = 300 m

Time = Distance ÷ Relative Speed

Time = 300 m ÷ 27.78 m/s ≈ 10.8 s