A 210 m long train crosses a man walking at a speed of 4.5 km/h in the opposite direction in 12 seconds. What is the speed (in km/h) of the train?

Correct option is D

Given:

Length of the train (Distance) = 210 m

time to cross = 12 second 

speed of the man = 4.5 km/h

Formula used:

Distance = Speed × time

When two bodies move in opposite direction

Then their relative speed = Sum of speeds

Solution:

Let the speed of the train be x km/h

Here, length of the train = 210m = $$\frac{210}{1000}$$​ = 0.21km [1km = 1000m]

Time = 12sec = $$\frac{12}{3600}$$​ = $$\frac{1}{300}$$​ hr       [As, 1 hour = 3600sec]

Speed of man = 4.5 km/h

As, they walk in opposite direction

Their relative speed = x + 4.5

Now, distance = speed × time

0.21 = ( x + 4.5) × $$\frac{1}{300}$$​​

63 = x + 4.5

x = 58.5 km/h 

Speed 58.5 km/h of the train