Question

A train travelling at 48 km hr completely crosses another train

Answer 1

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Let the length of the first train be x m 

Then, the length of second train is (x2)(x2) m.

Therefore, Relative speed = (48 + 42) km/h = (x2)(x2)

(90×518) m/s(90×518) m/s = 25 m/s 

According to the question, 

(x+x2)25=12(x+x2)25=12

=> 3x2=300=>x=200m3x2=300=>x=200m 

Therefore, Length of first train = 200 m 

Let the length of platform be y m. 

Speed of the first train 

= (48×518) m/s= 403 m/s(48×518) m/s= 403 m/s

Time=DistanceSpeedTime=DistanceSpeed

Therefore, (200+y)×340=45(200+y)×340=45

=> 600 + 3y = 1800

Therefore, y=400