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Motion In A Plane

Question
CBSEENPH11018607

Two trains travelling on the same track are approaching each other with the equal speed of 40 m/s. The drivers of the train begin to deaccelerate simultaneously when just 2.0 km apart. Assuming deacceleration to be uniform and equal, the value of the deacceleration to barely avoid collision should be? 

Solution
We have, 
Initial speed, u = 40 m/s 
Distance to be covered by each train before rest, s = 1000 m 
Acceleration, a = ? 
Using the relation, 
                  v2 = u2 + 2as
We have, 
straight a space equals space fraction numerator left parenthesis straight v squared space minus space straight u squared right parenthesis over denominator 2 straight s end fraction space
space space space equals space fraction numerator 0 space minus space left parenthesis 40 right parenthesis squared over denominator 2 space straight x space 1000 end fraction space

space space space equals space 0.8 space straight m divided by straight s squared