Question

Question 3.7 Two trains A and B of length 400 m each are moving on two parallel tracks with a uniform speed of 72 km h–1 in the same direction, with A ahead of B. The driver of B decides to overtake A and accelerates by 1 m/s2. If after 50 s, the guard of B just brushes past the driver of A, what was the original distance between them?

Class XI Physics Motion In A Straight Line Page 56

Answer 1

Heya !
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Lets considered their distance between them = s 

Speed of train A = Speed of train B = 72 km/h = 20 m/s

Time taken = 50 seconds to overtake 

Distance Travelled By train A = speed x time = 20 x 50 = 1000 m

ALso distance travelled by Train B (X) = ut + 1/2 at²

                                                             = 20 x 50  + 1/2 x 1 x 2500 

                                                             = 1000 (+ 1250  extra distance traveled                                                                            by train A ) 

Also Distance travelled by Train A = 800 + s 

Now , 

800 + s = 1250 

s           = 450 m