A train, 100 m long, is running at a speed of 64 km/h. Find the time taken by it to pass a man who is running at 8 km/h in the direction opposite to that of the train.

Length of the train = 100 m

Speed of the train = 64 km/h

Speed of the man = 8 km/h (opposite direction)

Relative speed=Speed of the train + Speed of the man

​$$\text{Time} = \frac{\text{Distance}}{\text{Relative speed}}$$​​

Relative speed = 64 + 8 = 72 km/h

Now, converting km/h into m/sec

$$72 \times \frac{5}{18}$$​ = 20 m/sec

So,

Time = $$\frac{100}{20}$$​ = 5 sec