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 s-2.
If after 50 s, the guard of B just brushes past the driver of A, what was the original distance between them ?
Hi Haroon,
I eventually worked out the answer. The original distance between the two trains should be equal to the distance travelled by train B in the 50 seconds.
Hi Haroon,
The confirmed answer I have is 1250m.
When we say the "distance between two trains A and B" it means this:
Hello everybody,
The correct Ans. = 1250m. Nishant's final answer is correct while the working seems confusing. Here is my version of the answer :
On looking at the question carefully, we find that the last line of the question tells us that the guard of train B brushes the driver of train A and asks us the distance between them - meaning orignal distance between the guard of train B and driver of train A.
Let the distance between the two trains be x [ dist. between driver of 'B' and guard of 'A' ]
So, original distance between the guard of 'B' and driver of 'A' = 400 + x + 400 =
distance travelled by train 'A' in 50s at a speed of 20ms-1,
SA = 20 * 50 = 1000m
Distance travelled by train 'B' :-
SB = 20 * 50 + 0.5 * 1 * 502
= 1000 + 1250
= 2250m
We know that the guard of 'B' is at the same positioon of driver of 'A'
The guard of 'B' has travelled a distance of x+ 800 (original distance) + 1000 (distance travelled by train A).
The total distance travelled by train B is 2250 meters - which is also the total distance travelled by the guard of B.
Hence 1800+x = 2250.
This gives x = 450. This is the distance between the driver of B and Guard of A.
Hence the original distance between the guard of B and Driver of A = 400 ( length of train B) + 450 + 400 (Length of train A) = 1250 m.
The ambiguity is : what needs to be considered as the distance between the trains ?
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