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Question

A 100 m long train crosses a man travelling at 5 km/h, in opposite direction, in 7.2 s. Then the velocity of the train is

A
40 km/h
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B
25 km/h
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C
20 km/h
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D
45 km/h
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Solution

The correct option is D 45 km/h
Let vT be the velocity of the train and vm be the velocity of man.
According to question
vm=5 km/h
Now, velocity of train w.r.t man is given by
vTm=vTvm=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)=12.5 ms1
v=45 km/h

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