If a 900 m long train crosses a 700 m long platform in 1 minute, then the speed of the train in kilometres per hour is:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 96 km/h
To cross a platform completely, a train must cover its own length plus the length of the platform: the front of the train travels from the start of the platform until the rear of the train leaves its far end. Speed in m/s is converted to km/h by multiplying by \(\frac{18}{5}\) (1 m/s \(=\frac{3600}{1000}\) km/h).
Distance covered \(=900+700=1600\) m
Time \(=1\) minute \(=60\) s
Speed \(\displaystyle =\frac{1600}{60}=\frac{80}{3}\) m/s
In km/h: \(\displaystyle \frac{80}{3}\times\frac{18}{5}=\) 96 km/h
Tip: \(\frac{80}{3}\) in Option (1) is the speed in m/s, not in km/h. Look at the unit the question asks for before marking a value you have worked out on the way.