A 100m long train crosses a man travelling at 5km/h, in opposite direction, in 7.2s. Then the velocity of the train is
A
40km/h
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B
25km/h
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C
20km/h
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D
45km/h
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Solution
The correct option is D45km/h Let vT be the velocity of the train and vm be the velocity of man.
According to question vm=5km/h
Now, velocity of train w.r.t man is given by vTm=vT−vm=vT−(−5) vT+5 (∵ man is travelling in opposite direction to that of the train)
Time =relative distancerelative speed 7.2=100(v+5)(518)=12.5ms−1 ⇒v=45km/h