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Question
A train is moving at a speed of 90 km/h. On applying brakes, a retardation of 2.5 ms-2 is created. At what distance before, should the driver apply the brakes to stop the train at the station?
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Solution
Initial speed of train = 90 km/hr
Speed of train imn m/s = ( 90 X 1000 )/3600 = 25 m/s.
Retardation of the train = 2.5 ms-2.
Final speed of train at platform = 0 m/s.
We know that v2 - u2 = 2as.
0 - 25 X25 = 2 X (-2.5) X s
S = 625/5 = 125 m.
So driver should apply the brakes 125 m before the platform.
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