A 120 m long train crosses a man walking at a speed of 8.5 km/h in the opposite direction in 12 seconds. What is the speed (in km/h) of the train?

Given:

A 120 m long train crosses a man walking at a speed of 8.5 km/h in the opposite direction in 12 seconds.

Formula used:

Relative Speed = (Speed of train (Vtrain) + Speed of man) km/h

Relative Speed = Distance / Time

Calculation:

Distance = 120 m = 0.12 km

Time = 12 seconds = 12/3600 hours = 1/300 hours

Relative Speed = 0.12 km / (1/300) hours

⇒ Relative Speed = 0.12 × 300

⇒ Relative Speed = 36 km/h

Speed of man = 8.5 km/h

V_train = Relative Speed - Speed of man

⇒ V_train = 36 km/h - 8.5 km/h

⇒ V_train = 27.5 km/h

∴ The correct answer is option 4.