a train passes two cars moving in the direction at 45km/hr and 50km/hr in 36 sec and
a train passes two cars moving in the direction at 45km/hr and 50km/hr in 36 sec and 54 sec respectively. What is the length of the train?
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smart kida train passes two cars moving in the direction at 45km/hr and 50km/hr in 36 sec and 54 sec respectively. What is the length of the train?

RajdeepCERe: a train passes two cars moving in the direction at 45km/hr and 50km/hr in 36 sec
Here we have two unknown variables of train : 1. Speed of Train , 2. Length of Train.
Say we have Car A running at 45km/hr & Car B at 50km/hr.
So basically train covers the following distance is both case,
Car A case => Train covers total of 450 + xm distance in 36 sec,
Car B casr => Train covers total of 750 + xm distance in 54 sec.
where x is the length of train.
So taking the difference of these two equantions, we are able to derive that train covers 300m distance in 18 sec, so speed of train is 60km/hr.
So now we can say that distance covered by train for the period of 36sec and 54 sec respectively is 600m and 900m.
And from that solving any of one equation we will get the length of train, which is 150m according to me. 
simplycoderRe: a train passes two cars moving in the direction at 45km/hr and 50km/hr in 36 sec
Let us assume::
the length of train is x km.
the velocity of the train is v km/h.
Case A:: Car A.
Velocity is 45km/h.
Time is 36 secs = 36/3600hr = 0.01 hr.
Since train crosses the cars, v is greater than velocity of car.
so the net velocity is (v45)kmph.
Distance=speed*time.
Here the distance covered is nothing but length of train.
Therefore
x = (v45)*0.01 ...............................(1)
Similarly from car 2:
x = (v50)*0.015...............................(2)
Divide and solve for v,from the above equations,
v=60 kmph.
put in (1).
x=(6045)*0.01
x=0.15 km
Hence x = 150 m
Therefore the length of train is 150 m. 
Prachi Verma
Plz solve this question
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