The Total solution for NCERT class 6-12
Two trains A and B of length 400 m each are moving on two parallel trackswith auniform speed of 72 km h–1 inthe same direction, with A ahead of B. The driver ofB decides to overtake A and acceleratesby 1 m s–2. If after 50 s, the guard of B justbrushes past the driver of A, what wasthe original distance between them?
Length of the train Aand B = 400 m
Speed of both thetrains = 72 km/h = 72 x (5/18) = 20m/s
Using the relation, s= ut + (1/2)at2
Distance covered bythe train B
SB = uBt+ (1/2)at2
Acceleration, a = 1m/s
Time = 50 s
SB =(20 x 50) + (1/2) x 1 x (50)2
= 2250 m
Ditance covered by thetrain A
SA = uAt+ (1/2)at2
Acceleration, a = 0
SA = uAt = 20 x 50 = 1000 m
Therefore, theoriginal distance between the two trains = SB – SA =2250 – 1000 = 1250 m