Question

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

Answer 1

Train A:-
Speed = 72km/h = 72×5/18 = 20 m/s
Time = 50 seconds
Distance = Speed × Time
= 20 × 50
= 1000 m
Train B:-
u = 72 km/h = 20 m/s
t = 50 seconds
a = 1 m/s²
s = ut + 1/2at²
= 20×50 + 1/2×1×(50)²
= 1000+ 1/2×2500
= 1000+1250
= 2250 m
Distance travelled more by train B = 2250-1000
= 1250 m
Length of 1 train = 400 m
Distance between them = 1250-400
= 850 m

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Answer 2

heyy !
____________________________________________________________
Train A : 
speed = 72 km / h = 20 m /s 
time    = 50 seconds 
Distance = speed X time 
               = 20 X 50 
               = 1000 m 

____________________________________________________________
Train B 
speed = 72 km/h = 20 m/ s
time    = 50 seconds 
acceleration = 1 m/s²
s = ut+1/2 at²
s = 20 x 50 + 1/2 X 1 X 50 X 50 
   = 1000 + 1250 
   = 2250 m 
Distance travelled more by train B = 2250 - 1000 
                                              = 1250 m 
distance between two trains  = 1250 - 400
because in this case we cant take train as a point object 
so ,distance between two trains = 850  m