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a train crosses Deepak& dilip in 20 seconds &30 seconds respectively who are running in same direction train at the speed of 18kmph and 36kmph respectively.find speed of the train
Asked by dhananjaydhanu80 | 27 Dec, 2018, 10:55: AM
answered-by-expert Expert Answer
Let speed of train = u m/s
running speed of Deepak = 18 km/hr = 5 m/s
running speed of Dilip = 36 km/hr = 10 m/s
 
Relative speed of train with respect to Deepak = ( u - 5 ) m/s
Relative speed of train with respect to Dilip = ( u - 10 ) m/s
 
Let l be the length of train.
 
Time taken by train to cross Deepak = l / (u-5) = 20  or  20u-100 = l  ......................(1)
Time taken by train to cross Dilip    = l / (u-10) = 30  or 30u - 300 = l  ....................(2)
 
By equating (1) and (2),  20u - 100 = 30u - 300 , we get u = 20 m/s
 
speed of train = 20 m/s = 72 km/hr
Answered by Thiyagarajan K | 27 Dec, 2018, 13:20: PM

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